Magnetoresistance effect element, magnetic head, magnetic head assembly, magnetic storage system

ABSTRACT

Disclosed are a high-sensitivity and high-reliability magnetoresistance effect device (MR device) in which bias point designing is easy, and also a magnetic head, a magnetic head assembly and a magnetic recording/reproducing system incorporating the MR device. In the MR device incorporating a spin valve film, the magnetization direction of the free layer is at a certain angle to the magnetization direction of a second ferromagnetic layer therein when the applied magnetic field is zero. In this, the pinned magnetic layer comprises a pair of ferromagnetic films as antiferromagnetically coupled to each other via a coupling film existing therebetween. The device is provided with a means of keeping the magnetization direction of either one of the pair of ferromagnetic films constituting the pinned magnetic layer, and with a nonmagnetic high-conductivity layer as disposed adjacent to a first ferromagnetic layer on the side opposite to the side on which the first ferromagnetic layer is contacted with a nonmagnetic spacer layer. With that constitution, the device has extremely high sensitivity, and the bias point in the device is well controlled.

FIELD OF THE INVENTION

[0001] The present invention relates to a magnetoresistance effectdevice, a magnetic head, a magnetic head assembly, and a magneticrecording/reproducing system. More precisely, it relates to amagnetoresistance effect device, a magnetic head, a magnetic headassembly, and a magnetic recording/reproducing system, in which is useda giant magnetoresistance effect element having high sensitivity andhigh reliability.

BACKGROUND OF THE INVENTION

[0002] The recent tendency in the art is toward small-sized,large-capacity magnetic recording media, for which there are increasinggreat expectations of high-power MR heads (magnetoresistance effectheads). For the MR film which is the basic constituent element in thoseMR heads, widely noticed is a spin valve film having a multi-layeredmagnetic film with a sandwich structure of magnetic layer/nonmagneticlayer/magnetic layer, in which one magnetic layer is pinned for itsmagnetization owing to the magnetic coupling bias applied thereto (thislayer may be referred to as a “pinned magnetic layer” or “pinned layer”)while the other magnetic layer is reversed for its magnetization owingto the applied magnetic field (this layer may be referred to as a “freemagnetic layer” or “free layer”). The spin valve film of that typeproduces a giant magnetoresistance effect (GMR) through the relativeangle change in the magnetization direction between those two magneticlayers.

[0003] As other types of MR films, known are an anisotropicmagnetoresistance effect film (AMR film) made of an NiFe alloy or thelike, an artificial lattice film, etc. Though smaller than that in anartificial lattice film, the MR ratio in a spin valve film is at least4% and is much larger than that in an AMR film. A spin valve film cansaturate its magnetization even in a low magnetic field, and istherefore suitable to MR heads. MR heads incorporating such a spin valvefilm receive much expectations for their practical applications.Specifically, for increasing the recording density in magnetic recordingon magnetic discs and the like, high-sensitivity GMR heads (giantmagnetoresistance effect heads) are indispensable.

[0004] Early GMR heads incorporate, in its GMR device, a spin valve filmthat comprises a free layer, a nonmagnetic spacer layer, a pinnedmagnetic layer and an antiferromagnetic layer. In those, the increase inthe sensitivity of the film is indispensable for increasing therecording density through reduction in the recording track width.However, if the free layer is thinned so as to increase the sensitivityof the film for that purpose, the stray magnetic field from the pinnedmagnetic layer will shift the bias point. In that case, it is oftendifficult to effectively correct the thus-shifted operating point by thecurrent magnetic field.

[0005] On the other hand, a so-called laminated pinned ferromagneticlayer (hereinafter referred to as “SyAF”, or “Synthetic AF”) has beenproposed (U.S. Pat. No. 5,465,185), which comprises two ferromagneticlayers as antiferromagnetically coupled via an antiferromagneticallycoupling layer existing therebetween. In principle, theantiferromagnetically-coupled, pinned layer of that type would producevery small stray magnetic field, thereby readily ensuring the operatingpoint.

[0006] One case of a spin valve film with SyAF is referred to, in whichone of the two ferromagnetic layers adjacent to the nonmagnetic spacerlayer is a ferromagnetic layer A while the other adjacent to theantiferromagnetic layer is a ferromagnetic layer B and in which theferromagnetic layer A and the ferromagnetic layer B have the samemagnetic thickness, thickness x saturation magnetization. In that case,the stray magnetic fields from the layer A and layer B cancel each otherso that there is substantially no stray magnetic field generated by thepinned layer. As a result, the pinned layer of that type is no moresusceptible to a magnetic field and has the significant advantage ofstable pinned magnetization at around the blocking temperature, Tb, atwhich the magnetic coupling bias of the antiferromagnetic layer is lost.

SUMMARY OF THE INVENTION

[0007] The problem with the present technology, that an object of thepresent invention is to resolve, is that the inventors found, the biaspoint designing in an applied sense current is difficult, especially indevice using thin free layer so as to increase the sensitivity of outputsignal for high density recording.

[0008] In a first aspect, the present invention provide amagnetoresistance effect element that attains the object mentioned abovecomprising a nonmagnetic spacer layer, a first ferromagnetic layer and asecond ferromagnetic layer as separated by the nonmagnetic spacer layer,in which the first ferromagnetic layer has a magnetization directiondifferent from the magnetization direction of the second ferromagneticlayer when the applied magnetic field is zero, and the secondferromagnetic layer comprises a pair of ferromagnetic films asantiferromagnetically coupled to each other and a coupling film thatseparates the pair of ferromagnetic films while antiferromagneticallycoupling them, and a nonmagnetic high-conductivity layer adjacent to thefirst ferromagnetic layer on the plane opposite to the plane at whichthe first ferromagnetic layer is contacted with the nonmagnetic spacerlayer.

[0009] In the present invention, the magnetoresistance effect device mayrealize extremely high sensitivity while maintaining a good bias point.Preferably, the MR device may be in the form of a so-called spin valvedevice (see U.S. Pat. No. 5,206,590), in which the first ferromagneticlayer is not coupled to the second ferromagnetic layer and themagnetization directions of the two layers are perpendicular to eachother at zero applied magnetic field. Preferably, the applied magneticfield to change the magnetization of the first ferromagnetic layer maybe smaller than that to change the magnetization of the secondferromagnetic layer, and the magnetization of the second ferromagneticlayer is pinned to such a degree that the magnetization direction maynot change even in the presence of an applied magnetic field.

[0010] In the present invention, the nonmagnetic high-conductivity layermay contain an element of which the specific resistance in bulk at roomtemperature is not larger than 10 μΩcm, thereby realizing goodcharacteristic, namely, high MR ratio owing to the spin filter effect inthe ultra-thin first ferromagnetic layer and low Hcu.

[0011] For high density recording and for realizing the increase in MRratio owing to the spin filter effect of the nonmagnetichigh-conductivity layer, the thickness of the first ferromagnetic layermay be between 0.5 nanometers and 4.5 nanometers.

[0012] In the present invention, the thickness of the nonmagnetichigh-conductivity layer and that of the second ferromagnetic layer maybe so designed that the wave asymmetry, (V1−V2)/(V1+V2), in which V1indicates the peak value of the reproduction output in a positive signalfield and V2 indicates the peak value of the reproduction output in anegative signal field, may fall between minus 0.1 and plus 0.1.

[0013] In the present invention, the MR device may satisfy theconditions of 0.5 nanometers≦tm(pin1)−tm(pin2)+t(HCL)≦4 nanometers andt(HCL)≧0.5 nanometers, in which t(HCL) indicates the thickness of thenonmagnetic high-conductivity layer (in terms of the Cu layer having aspecific resistance of 10 μΩcm), and tm(pin1) and tm(pin2) indicate themagnetic thicknesses of the pair of ferromagnetic films, respectively,in the second ferromagnetic layer in terms of saturation magnetizationof 1 Tesla, where pin 1 is of one of the ferromagnetic films disposedadjacent to the nonmagnetic spacer layer and pin2 is of another one ofthe ferromagnetic films. Satisfying the conditions noted above, the MRdevice may realize the wave asymmetry falling between minus 0.1 and plus0.1 and high MR.

[0014] In the present invention, the first ferromagnetic layer may havea magnetic thickness, thickness×saturation magnetization, of smallerthan 4.5 nanometer Tesla.

[0015] In the present invention, the nonmagnetic high-conductivity layermay be of a metal film that contains at least one metal element selectedfrom the group consisting of copper (Cu), gold (Au), silver (Ag),ruthenium (Ru), iridium (Ir), rhenium (Re), rhodium (Rh), platinum (Pt),palladium (Pd), aluminium (Al), osmium (Os) and nickel (Ni), all ofwhich are advantageous for meeting the condition of realizing low Hin.

[0016] In the present invention, the nonmagnetic high-conductivity layermay have a laminate film composed of at least two layers, for attaininglow Hin and soft magnetic characteristics control. In the presentinvention, in the laminate film, the layer adjacent to the firstferromagnetic layer may contain copper (Cu) which is especially suitablefor realizing high MR ratio, low Hcu and soft magnetic characteristics.In the laminate film, the layer not adjacent to the first ferromagneticlayer may contain at least one element selected from the groupconsisting of ruthenium (Ru), rhenium (Re), rhodium (Rh), palladium(Pd), platinum (Pt), iridium (Ir) and osmium (Os) all of which areespecially suitable for realizing low Hin, low Hcu and soft magneticcharacteristics control.

[0017] In the present invention, the nonmagnetic high-conductivity layermay have a thickness of from 0.5 nanometers to 5 nanometers and theelement may realize low Hcu and high MR ratio.

[0018] In the present invention, the layer that is contacted with thenonmagnetic high-conductivity layer at the plane opposite to the planeat which the nonmagnetic high-conductivity layer is contacted with thefirst ferromagnetic layer may contain at least one element selected fromthe group consisting of tantalum (Ta), titanium (Ti), zirconium (Zr),tungsten (W), hafnium (Hf), molybdenum (Mo), and chromium (Cr), and thedevice may realize low Hin and high MR ratio.

[0019] In the present invention, the first ferromagnetic layer may be ofa laminate film that comprises an alloy layer containing nickel iron(NiFe) and a layer containing cobalt (Co) and the device may realizehigh MR ratio and soft magnetic characteristics.

[0020] In the present invention, the first ferromagnetic layer may be analloy layer containing cobalt iron (CoFe) and the element may realizehigh MR ratio and soft magnetic characteristics.

[0021] In the present invention, for pinning the magnetization directionof the second ferromagnetic layer, an antiferromagnetic layer may belaminated over the layer.

[0022] In the present invention, for realizing still high MR ratio evenafter thermal treatment in its production, the antiferromagnetic layermay be made of a material, XzMnl-z in which X indicates at least oneelement selected from the group consisting of iridium (Ir), ruthenium(Ru) rhodium (Rh), platinum (Pt), palladium (Pd) and rhenium (Re) andthe compositional factor z falls between 5 atm. % and 40 atm. %, in thepresent invention.

[0023] In the present invention, the antiferromagnetic layer may be madeof a material, XzMnl-z in which X indicates at least one elementselected from the group consisting of platinum (Pt) and palladium (Pd)and the compositional factor z falls between 40 atm. % and 65 atm. %,and the element may maintain high MR ratio.

[0024] In the present invention, the nonmagnetic spacer may be of ametal layer containing copper (Cu) and its thickness maybe between 1.5nanometers and 2.5 nanometers and the element may realize high MR ratiofor more efficiently utilizing the effect of high MR ratio by thenonmagnetic high-conductivity layer, and may also realize low Hcu.

[0025] In the present invention, the pair of ferromagnetic films asantiferromagnetically coupled to each other may have the same thicknessand the difference in the magnetic thickness, thickness×saturationmagnetization, between the pair of ferromagnetic films may fall between0 nanometer Tesla and 3 nanometer Tesla, and the element may realizehigh MR, improved ESD resistance, and the thermal stability of thesecond ferromagnetic layer.

[0026] In the present invention, the antiferromagnetically layercoupling the pair of ferromagnetic films to each other may comprise Ruand its thickness may fall between 0.8 nanometers and 1.2 nanometers.

[0027] In a second aspect, the present invention provides amagnetoresistance effect device comprising a nonmagnetic spacer layer, afirst ferromagnetic layer and a second ferromagnetic layer as separatedby the nonmagnetic spacer layer, in which the magnetization direction ofthe first ferromagnetic layer differs from that of the secondferromagnetic layer when the applied magnetic field is zero, and anonmagnetic high-conductivity layer adjacent to the first ferromagneticlayer on the plane opposite to the plane at which the firstferromagnetic layer is contactedwith the nonmagnetic spacer layer, inwhich the thickness of the nonmagnetic high-conductivity layer and thethickness of the ferromagnetic layer are so designed that the waveasymmetry, (V1−V2)/(V1+V2), in which V1 indicates the peak value of thereproduction output in a positive signal field and V2 indicates the peakvalue of the reproduction output in a negative signal field, fallsbetween minus 0.1 and plus 0.1.

[0028] For attaining the wave asymmetry of falling between minus 0.1 andplus 0.1, it may not be always necessary to employ the constitution ofSyAF in the device but also a single layer. In that case, it isdesirable that the second ferromagnetic layer of a single layer may havea magnetic thickness of from 0.5 nanometer Tesla to 3.6 nanometer Tesla.If the magnetic thickness of the single layer of the secondferromagnetic layer is larger than 3.6 nanometer Tesla, it may bedifficult to attain the wave asymmetry noted above. On the other hand,if it is smaller than 0.5 nanometer Tesla, the MR ratio in the devicewill be noticeably small.

[0029] In a third aspect, the present invention provides amagnetoresistance effect device comprising a nonmagnetic spacer layer,first and second ferromagnetic layers separated by the nonmagneticspacer layer, in which the magnetization direction of the firstferromagnetic layer differs from that of the second ferromagnetic layerwhen the applied magnetic field is zero, and a nonmagnetichigh-conductivity layer adjacent to the first ferromagnetic layer on theplane opposite to the plane at which the first ferromagnetic layer iscontacted with the nonmagnetic spacer layer and that the devicesatisfies the conditions of 0.5 nanometers <tm(pin)+t(HCL)≦4 nanometersand t(HCL)≧0.5 nanometers, in which t(HCL) indicates the thickness ofthe nonmagnetic high-conductivity layer in terms of copper having aspecific resistance of 10 μΩcm, and tm(pin) indicates the magneticthicknesses of the second ferromagnetic layer, respectively, in thesecond ferromagnetic layer in terms of saturation magnetization of 1Tesla.

[0030] Satisfying the conditions noted above, the MR device may realizethe wave asymmetry falling between minus 0.1 and plus 0.1 and high MR,even when the second ferromagnetic layer therein is a single layer.

[0031] In a fourth aspect, the present invention provides amagnetoresistance effect device comprising a pinned magnetic layer and afree layer as separated by a nonmagnetic spacer layer disposedtherebetween, and an antiferromagnetic layer as laminated on the pinnedmagnetic layer for pinning the magnetization of the pinned magneticlayer, the pinned magnetic layer comprises a pair of ferromagneticlayers, a ferromagnetic layer A as disposed adjacent to the nonmagneticspacer layer and a ferromagnetic layer B as disposed adjacent to theantiferromagnetic layer, that those ferromagnetic layers A and B areantiferromagnetically coupled to each other via an antiferromagneticallycoupling layer existing therebetween, and that the close-packed plane ofthe antiferromagnetic layer is so oriented that the half-value width ofthe diffraction peak from the closed packed plane of the layer in itsrocking curve appears at 8° or smaller.

[0032] In a fifth aspect, the present invention provides amagnetoresistance effect element comprising a nonmagnetic spacer layer,and first and second ferromagnetic layers separated by the nonmagneticspacer layer, a magnetization direction of the first ferromagnetic layerbeing at an angle relative to a magnetization direction of the secondferromagnetic layer at zero applied magnetic field, the secondferromagnetic layer comprising first and second ferromagnetic filmsantiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically so that theirmagnetizations are aligned antiparallel with one another and remainantiparallel in the presence of an applied magnetic field, themagnetization of the first ferromagnetic layer freely rotating in signalmagnetic field. The element further comprises a pair of electrodescoupled to the magnetoresistance effect film and having respective inneredges; and a pair of longitudinal biasing layers for providing biasmagnetic fields to the first ferromagnetic layer in parallel with alongitudinal direction of the first ferromagnetic layer and havingrespective inner edges, wherein the inner edges of the pair ofelectrodes are disposed between the inner edges of the pair oflongitudinal biasing layers.

[0033] In a sixth aspect, the present invention provides amagnetoresistance effect device comprising a spin valve film and a pairof electrodes for supplying sense current to the spin valve film, inwhich the spin valve film comprises at least one nonmagnetic spacerlayer and at least two magnetic layers as separated by the nonmagneticspacer layer existing therebetween. The spin valve film is provided witha magnetoresistance effect-improving layer of being a laminate film of aplurality of metal films as disposed adjacent to the magnetic layer onthe plane opposite to the plane at which the nonmagnetic spacer layer iscontacted with the magnetic layer, and with a nonmagnetic layer actingas a underlayer or a protecting layer as disposed adjacent to themagnetoresistance effect-improving layer on the plane opposite to theplane at which the magnetic layer is contacted with themagnetoresistance effect-improving layer, and that the elementessentially constituting the metal film of the magnetoresistanceeffect-improving layer that is adjacent to the magnetic layer does notform a solid solution with the element essentially constituting themagnetic layer.

[0034] In the above descried element, the magnetoresistanceeffect-improving layer may exhibit, as its one capability as follows. Inthe device in which the free layer is thin, the magnetoresistanceeffect-improving layer acts as a nonmagnetic high-conductivity layersuch as that mentioned above. In this, the interface between theultra-thin free layer and the nonmagnetic high-conductivity layer isformed of a combination of materials not producing a solid solutiontherein, thereby preventing any diffusive scattering of electrons in theinterface so as to improve the up-spin transmittance. With thatconstitution, the device maintains high MR ratio therein. As not havinga solid solution phase, the interface is stable to thermal treatment anddoes not cause the reduction in MR ratio in the device. Themagnetoresistance effect-improving layer exhibits its ability to improvethe magnetoresistance effect of the device, while being based not onlyon its spin filter capability but also on its additional capabilities tocontrol the microcrystal structure of the spin valve film and to reducethe magnetostriction in the film.

[0035] In one specific example, the magnetic layer adjacent to themagnetoresistance effect-improving layer may be made of Co or a Coalloy, the magnetoresistance effect-improving layer may comprise atleast one element selected from Cu, Au and Ag. In another example of thedevice where the magnetic layer adjacent to the magnetoresistanceeffect-improving layer may be made of an Ni alloy, the magnetoresistanceeffect-improving layer may comprise at least one element selected fromRu, Ag, Cu, and Au. In the device, the magnetoresistanceeffect-improving layer may comprise any one or more elements of Cu, Au,Ag, Pt, Rh, Ru, Al, Ti, Zn, Hf, Pd, Ir, etc.

[0036] The magnetoresistance effect device of the invention is based onthe technique of reducing the magnetostriction in the CoFe alloys andothers noted above by or Au/Cu laminate film, Ru/Cu laminate film, orAu—Cu alloys. Specifically, the device comprises a spin valve film and apair of electrodes for supplying sense current to the spin valve film,in which the spin valve film comprises one nonmagnetic spacer layer andtwo magnetic layers as separated by the nonmagnetic spacer layerexisting therebetween, and this is characterized in that, of at leasttwo magnetic layers, one of which the magnetization direction varies,depending on the applied magnetic field, is oriented to fcc(111), andthat the d(111) lattice spacing is between 0.2055 and 0.2035 nanometers.

[0037] In a seventh aspect, the present invention provides amagnetoresistance effect device comprising a giant magnetoresistanceeffect film and a pair of electrodes for supplying current to the giantmagnetoresistance effect film, in which the giant magnetoresistanceeffect film comprises at least a pair of a pinned magnetic layer and afree layer as separated by a nonmagnetic spacer layer disposedtherebetween, and an antiferromagnetic layer as laminated on the pinnedmagnetic layer for pinning the magnetization of the pinned magneticlayer, and which is characterized in that the pinned magnetic layercomprises a pair of ferromagnetic layers, a ferromagnetic layer A asdisposed adjacent to the nonmagnetic spacer layer and a ferromagneticlayer B as disposed adjacent to the antiferromagnetic layer, that thoseferromagnetic layers A and B are antiferromagnetically coupled to eachother via an antiferromagnetically coupling layer existing therebetween,and that the antiferromagnetic layer has a thickness of at most 20nanometers and has a magnetic coupling coefficient, J, for theferromagnetic layer B of at least 0.02 erg/cm² at 200° C.

[0038] In an eighth aspect, the present invention provides amagnetoresistance effect element comprising a giant magnetoresistanceeffect film and a pair of electrodes for supplying current to the giantmagnetoresistance effect film, in which the giant magnetoresistanceeffect film comprises at least a pair of a pinned magnetic layer and afree layer as separated by a nonmagnetic spacer layer disposedtherebetween, and an antiferromagnetic layer as laminated on the pinnedmagnetic layer for pinning the magnetization of the pinned magneticlayer, the pinned magnetic layer comprises a pair of ferromagneticlayers, a ferromagnetic layer A as disposed adjacent to the nonmagneticspacer layer and a ferromagnetic layer B as disposed adjacent to theantiferromagnetic layer, those ferromagnetic layers A and B areantiferromagnetically coupled to each other via an antiferromagneticallycoupling layer existing therebetween, and the antiferromagnetic layerhas a thickness of at most 20 nanometers and contains at least any oneof Z_(x)Mn_(1-x) (where Z is at least one selected from Ir, Rh, Ru, Pt,Pd, Co and Ni, and 0<x<0.4), Z_(x)Mn_(1-x) (where Z is at least oneselected from Pt, Pd and Ni, and 0.4≦x≦0.7), or Z_(x)Cr_(1-x) (where Zis at least one selected from Mn, Al, Pt, Pd, Cu, Au, Ag, Rh, Ir and Ru,and 0<x<1).

[0039] The magnetic head and the magnetic recording/reproducing systemof the invention incorporate the magnetoresistance effect device of theinvention noted above. Specifically, the magnetic head of the inventionis characterized by comprising a lower magnetic shield layer, amagnetoresistance effect device of the invention such as that notedabove, which is formed on the lower magnetic shield layer via a lowerreproducing magnetic gap therebetween, and an upper magnetic shieldlayer as formed on the magnetoresistance effect device via an upperreproducing magnetic gap therebetween.

[0040] The magnetic head for separated recording/reproducing of theinvention is provided with a reproducing head that comprises a lowermagnetic shield layer, a magnetoresistance effect device of theinvention such as that noted above, which is formed on the lowermagnetic shield layer via a lower reproducing magnetic gap therebetween,and an upper magnetic shield layer as formed on the magnetoresistanceeffect device via an upper reproducing magnetic gap therebetween, andwith a recording head that comprises a lower magnetic pole which iscommon to the upper magnetic shield layer, a recording magnetic gap asformed on the lower magnetic pole, and an upper magnetic pole as formedon the recording magnetic gap.

[0041] The magnetic head assembly of the invention is characterized bycomprising a head slider having the separated recording/reproducingmagnetic head of the invention noted above, and an arm having asuspension on which the head slider is mounted. The magneticrecording/reproducing system of the invention is characterized bycomprising a magnetic recording medium, and a head slider provided withthe separated recording/reproducing magnetic head of the invention notedabove with which signals are written on the magnetic recording medium ina magnetic field and signals are read in the magnetic field as generatedby the magnetic recording medium.

[0042] The magnetoresistance effect device of the invention mentionedabove is applicable not only to magnetoresistance effect heads but alsoto magnetoresistance effect sensors.

[0043] Any one of the present invention may be provided not only in discdrive system but also other magnetic storage system, such as magneticmemory device. The magnetic disc drive system of the invention ischaracterized in that a current is applied to the magnetoresistanceeffect device in the magnetoresistance effect head to generate amagnetic field and that the system is provided with a mechanism capableof pinning the magnetization of the pinned magnetic layer in apredetermined direction in the thus-generated magnetic field.

[0044] Method for producing the magnetoresistance effect elements of theinvention comprises heating the pair of ferromagnetic film A and theferromagnetic film B of the synthetic pinned layer in a magnetic field,after the film of the giant magnetoresistance effect device has beenformed but before it is patterned, thereby pinning the magnetization ofthe pinned magnetic layer in a predetermined direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] A more complete appreciation of the invention and many of theattendant advantage thereof is readily obtained as the same necomesbetter understood by reference to the following detailed descriptionwhen electrode in connection with the accompanying drawings, wherein:

[0046]FIG. 1 is a sectional view for explaining the film constitution ofthe first magnetoresistance effect device of the invention.

[0047]FIG. 2 is a transfer curve given by the first magnetoresistanceeffect device of the invention.

[0048]FIG. 3 is a graph of the Cu thickness of the high-conductivitylayer adjacent to the free layer on the side opposite to the side atwhich the spacer is contacted with the free layer, versus the currentmagnetic field Hcu applied to the free layer.

[0049]FIG. 4 is a graph concretely showing the range of the pinned layerthickness and the nonmagnetic high-conductivity layer thickness forrealizing asymmetry of from −10% to +10%, or that is, for realizing biaspoints of from 30% to 50%.

[0050]FIG. 5 is a sectional view of a typical film constitution of thefirst embodiment of the magnetoresistance effect device of theinvention.

[0051]FIG. 6 is a sectional view of a film constitution of the spinvalve film of one example of the invention.

[0052]FIG. 7A and FIG. 7B are conceptual views for explaining twoproblems with conventional magnetoresistance effect devices.

[0053]FIG. 8 is a graph of calculated bias point values versus headreproducing signal waves.

[0054]FIG. 9 is an explanatory view indicating magnetic fields acting ona free layer.

[0055]FIG. 10 is a sectional view of a magnetoresistance effect film, inwhich are shown current flows I₁ to I₃ running through the layers.

[0056]FIG. 11 is a conceptual view showing the condition of the biaspoint in Comparative Case 1.

[0057]FIG. 12 is a conceptual view of the bias point versus Hin, Hpinand Hcu on a transfer curve.

[0058]FIG. 13 is a conceptual view showing the determinant factors forthe bias point in Comparative Case 3.

[0059]FIG. 14 is a conceptual view showing the determinant factors forthe bias point in Comparative Case 4.

[0060]FIG. 15 is a graph of the free layer thickness dependence of thebias point in the spin valve films of the invention, as compared withthat in the spin valve films of Comparative Cases.

[0061]FIG. 16 is a graph of the MR ratio in the structures ofComparative Cases 1 to 4 with the product of Ms×t only in the free layerbeing reduced.

[0062]FIG. 17 is a sectional view of one embodiment of themagnetoresistance effect head of the invention.

[0063]FIG. 18 is a schematic view of the magnetic coupling bias fieldHUA* versus the change in the resistance, R, of the spin valve filmdepending on the applied magnetic field.

[0064]FIG. 19 is a graph of the angle of movement of the magnetizationof the pinned magnetic layer, versus time, in the presence of asimulation bias field.

[0065]FIG. 20 shows the data of the half-value width of the diffractionpeak from the close-packed plane of an antiferromagnetic layer in itsrocking curve.

[0066]FIG. 21 is a graph of residual magnetization ratio, Mr/Ms,indicating the reduction in the antiferromagnetic coupling capability ofthe antiferromagnetically coupling layer of Ru after thermal treatment,relative to the thickness of the Ru layer.

[0067]FIG. 22A, FIG. 22B and FIG. 22C are graphs of resistance change inspin valve films versus the applied magnetic field.

[0068]FIG. 23A, FIG. 23B and FIG. 23C are graphs of resistance change inspin valve films with the thicknesses of the ferromagnetic layer A andferromagnetic layer B being varied, versus the applied magnetic field.

[0069]FIG. 24A and FIG. 24B are graphs of resistance versus output in aspin valve device to which has been applied a simulation ESD voltage bya human body model.

[0070]FIG. 25A and FIG. 25B are graphs of resistance versus output inanother spin valve device to which has been applied a simulation ESDvoltage by a human body model.

[0071]FIG. 26 is a perspective view of a spin valve film, indicating thestray magnetic field from the film.

[0072]FIG. 27 is a sectional view of another embodiment of themagnetoresistance effect head of the invention.

[0073]FIG. 28 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

[0074]FIG. 29 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

[0075]FIG. 30 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

[0076]FIG. 31 is a sectional view of still another embodiment of themagnetoresistance effect head of the invention.

[0077]FIG. 32 is a sectional view of the essential structure of oneembodiment of the magnetoresistance effect device of the invention.

[0078]FIG. 33 is a sectional view of one modification of the embodimentof the magnetoresistance effect device of FIG. 32.

[0079]FIG. 34 is a sectional view of another modification of theembodiment of the magnetoresistance effect device of FIG. 32.

[0080]FIG. 35A, FIG. 35B and FIG. 35C are views showing the reduction inthe MR ratio in conventional spin valve films after thermal treatment.

[0081]FIG. 36 is a view explaining specular reflection on metal/metalinterface.

[0082]FIG. 37A and FIG. 37B are graphs showing two examples of therelationship between the ratio of the Fermi wavelength in a reflectivefilm to the Fermi wavelength in a GMR film adjacent to the reflectivefilm, and the critical angle θc.

[0083]FIG. 38 is a graph of the data of the critical angle θc at whichAu (Ag) /Cu interface produces specular reflection, as calculated fromthe Fermi wavelength at the interface.

[0084]FIG. 39 is a sectional view of still another modification of themagnetoresistance effect device of FIG. 32.

[0085]FIG. 40 is a sectional view of one modification of themagnetoresistance effect device of FIG. 39.

[0086]FIG. 41 is a sectional view of the essential part of the secondembodiment of the magnetoresistance effect device of the invention.

[0087]FIG. 42 is a sectional view of one modification of themagnetoresistance effect device of FIG. 41.

[0088]FIG. 43 is a sectional view of the essential part of the thirdembodiment of the magnetoresistance effect device of the invention.

[0089]FIG. 44 is a sectional view of the structure of the firstembodiment of a separated recording/reproducing magnetic head whichincorporates the magnetoresistance effect device of the invention.

[0090]FIG. 45 is a sectional view of the structure of the secondembodiment of a separated recording/reproducing magnetic head whichincorporates the magnetoresistance effect device of the invention.

[0091]FIG. 46 is a perspective view of the structure of one embodimentof a magnetic head assembly which incorporates the separatedrecording/reproducing magnetic head of the invention.

[0092]FIG. 47 is a perspective view of the structure of one embodimentof a magnetic disc system which incorporates the separatedrecording/reproducing magnetic head of the invention.

[0093]FIG. 48 is a graph of an XRD pattern of the spin valve film asproduced in Example 1 of the invention.

[0094]FIG. 49 is a sectional view of the essential part of oneembodiment of an artificial lattice film which incorporates themagnetoresistance effect device of the invention.

[0095]FIG. 50 is a conceptual view showing the cross section of a spinvalve device part as seen from its ABS (air baring surface). ABS maycomprise a protective film formed thereon.

[0096]FIG. 51 is a perspective view of a spin valve device with its gapfilm and shield film being removed.

[0097]FIG. 52 is a conceptual view of one embodiment of a head which issuitable to the top-type spin valve film of FIG. 1 and FIG. 5.

[0098]FIG. 53 is a graph of the data of nano-EDX analysis of the crosssection of a magnetic head which incorporates the magnetoresistanceeffect device of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0099] Embodiments of the invention are described in detail hereunderwith reference to the drawings.

[0100] First Embodiment:

[0101] First mentioned is the embodiment of the invention in which thefree layer (first ferromagnetic layer) is thinned.

[0102] The problems with the technique of “thinning the free layer”which the present inventors have recognized in the process of achievingthis embodiment of the invention are described in detail.

[0103] As so mentioned hereinabove, remarkable increase in thesensitivity of magnetoresistance effect devices is realized not only byincreasing the MR ratio but also by reducing the thickness of the freelayer (that is, by reducing the product of Ms×t). In a broad way, theoutput increases, being in reverse proportion to the product of Ms×t ofthe free layer. However, the present inventors' own investigations haveverified that the technique of thinning the free layer brings about thefollowing problems.

[0104] The first problem is that the bias point designing in an appliedsense current is difficult. When all the magnetic fields applied to thefree layer being driven are summed up and when the bias point is in thecenter of the linear inclination of a transfer curve, the biasingcondition will be the best. However, when the free layer is thinned, theinclination of the transfer curve becomes steep. In that condition, itis extremely difficult to lead the bias point to the center of thelinear region of the transfer curve. In a bad bias point condition,asymmetric signals will be formed, and in a worse condition, no outputlevel could be taken.

[0105] The second problem is that, if the free layer is thinned to anextreme degree according to a prior art technique, the MR ratio isgreatly lowered. The reduction in the MR ratio causes the reduction inthe reproducing output.

[0106]FIG. 7A and FIG. 7B are conceptual views for explaining the twoproblems with conventional magnetoresistance effect devices. In thosedrawings, shown are the transfer curves of magnetic heads each having amagnetoresistance effect device. FIG. 7A shows one case where the freelayer is thick; and FIG. 7B shows another case where the free layer isthin. As mentioned above, when the free layer is thinned, theinclination of the transfer curve becomes steep (that is, Hs becomessmall), and the MR ratio decreases. As a result, AV becomes small. FromFIG. 7A and FIG. 7B, known are the two problems noted above.

[0107] Of the two problems, one relating to the bias point could not berecognized with ease even though the film structure is determined.Therefore, film structure designing was extremely difficult. This time,we, the present inventors carried out various simulations, and correctedthe errors in the data we obtained, on the basis of our experiences. Asa result, we have succeeded in correct judgment of the bias point. Thecalculation of the bias point is mentioned below.

[0108] The bias point is shifted by various external magnetic fieldsapplied to the free layer. The shift could approximate the sum total of(1) current magnetic field (Hcu), (2) the static magnetic field from thepinned layer (Hpin), (3) the interlayer coupling magnetic field from thepinned layer via a spacer (Hin), and (4) the stray magnetic field(Hhard) from the hard bias film for the purpose of imparting alongitudinal bias to the magnetoresistance effect film. Of thosemagnetic fields (1) to (4), the hard bias magnetic field (4) isrelatively small. Having noted the sum of the magnetic fields (1) to(3), we, the present inventors have assiduously studied. The calculationformulae for the bias point which we employed this time are mentionedbelow.

B.P.=50×(Hshift/Hs)+50  (1-1)

Hshift=−Hin+Hpin+Hcu  (1-2)

Hs=Hd ^(free) +Hk(1-3)

Hd _(free)=π²(MS×t)_(free) /h  (1-3-1)

Hpin=π ² (Ms×t)_(pin) /h  (1-4)

Hcu=2πC×I _(s) /h  (1-5)

C=(I ₁ −I ₃)/(I ₁ +I ₂ +I ₃)  (1-5-1)

[0109] B.P. to be represented by the formula (1-1) is the bias point [%]to be specifically noted herein. The best bias point is 50%. Includingthe margin, the practicable range of the bias point will fall between 40and 60%. If the bias point oversteps the range, asymmetric signals willbe formed. In worse cases, no output could be obtainable.

[0110] Regarding the relationship between the bias point value and theasymmetry, the asymmetry will be +10% or so when the bias point is 40%,and it will be -10% or so when the bias point is 60%. As will bementioned hereunder, the best bias point in calculation does not fallbetween 40 and 60%, but falls between 30 and 50% in experiences.

[0111]FIG. 8 is a graph of calculated bias point values versus headreproducing signal waves. As shown, when the bias point falls between 30and 50%, the asymmetry is relatively small, and the signal profiles aregood. However, when the bias point is outside the range, the asymmetrybecomes great, as in FIG. 8, and the signal profiles are notpracticable.

[0112] As in the formula (1-2), Hshift, is the sum of the magneticfields [Oe] applied to the free layer. As in FIG. 7, Hs is theinclination of the transfer curve.

[0113]FIG. 9 is an explanatory view indicating magnetic fields acting onthe free layer.

[0114] Hd^(free) is an antimagnetic field for the free layer at acertainMR height. h is the MR height [μm]. Hpin is the pinned layerstray magnetic field from the pinned layer to the free layer.(Ms×t)_(free) is the product of the total saturation magnetization, Ms,and the thickness, t, of the free layer. (Ms×t)_(pin) is the product ofthe saturation magnetization and the thickness of the net pinned layer(for Synthetic AF, the difference in the magnetic thickness between theupper and lower pinned layers).

[0115] Hcu is the current magnetic field applied to the free layer. Isis the sense current [mA]. The coefficient, C, in the formula (1-5-1) isthe ratio of the partial current flow running through the upper layeroverlying the free layer to that running through the lower layerunderlying it.

[0116]FIG. 10 is a conceptual view indicating the partial current flowsI₁ to I₃ running through the layers.

[0117] For simplifying the calculation, the influences of the edges ofthe ABS plane and those of shields are not taken into consideration. Inour experiences, we, the present inventors have found that the biaspoint values as estimated in calculation are shifted to the minus sideby about 10% from those in actual heads. Considering the fact that theusable bias point range falls plus/minus 10% of the best bias pointvalue, it can be said that the good bias point range will fall between30% and 50% to be obtained in calculation. Accordingly, when the biaspoint falls between 30% and 50%, as obtained according to thecalculation shown above, it could be judged that the bias point valueswithin the range are good for practical use.

[0118] The problems with some conventional spin valve films aredescribed in detail hereunder, with reference to the bias pointcalculation formulae mentioned above.

[0119] Comparative Case 1: Ordinary Spin Valve (with NeitherHigh-conductivity Film nor Synthetic AF)

5 nanometer Ta/2 nm NiFe/0.5 nm Co/2 nm Cu/2 nm CoFe/7 nm IrMn/5nanometer Ta  (1)

[0120] The formula (1) indicates the laminate structure of the spinvalve, in which are shown the elements constituting the layers and theirthicknesses (nanometers). The film of this Comparative Case is amodification of a prior art spin valve film in which only the free filmis thinned. The bias points in this film constitution are calculated.

[0121] Of the bias point formulae (1-1) to (1-5) noted above, thecurrent magnetic field of the formula (1-5) is the most difficult toobtain. This is because the current flow ratio, C, of the formula(1-5-1) is difficult to obtain. In the thinned film, the specificresistance of each layer is influenced by the crystallinity and thecurrent distribution, and significantly differs from the specificresistance of the bulk. For practicable calculation as much as possible,we, the present inventors took the following measure and succeeded inobtaining the accurate current flow ratio, C.

[0122] For obtaining the specific resistance of each layer, a spin valvefilm sample having the constitution noted above is prepared. Forobtaining the specific resistance of a predetermined layer, a fewsamples in which the thickness of the layer is varied by plus/minus 2nanometers are prepared. In those samples, the relationship between thethickness of the layer and the conductance is obtained through linearextrapolation. The reason for the process is because actual data couldnot be obtained according to the well-known technique of obtaining thespecific resistance of thin, single-layer films. In order to minimizethe influences of crystallinity and those of current distribution, we,the present inventors have found through our experiments that the bestway for accurate determination is to prepare film samples in which eventhe overlying and underlying layers are of practicable materials and todetermine the conductance difference within the small thickness range asmentioned above.

[0123] The specific resistance of each layer as obtained according tothe method is influenced little by the crystallinity and, in addition,could cancel the influences of current distribution thereon. Therefore,the data of the current flow ratio, C, of the formula (1-5-1) obtainedaccording to this method are much more accurate than those obtained in asimple conductor in which is used the specific resistance ofsingle-layer films. According to the method, it has become possible tocalculate and estimate the current magnetic field with high accuracy,which, however, is difficult in the prior art technique.

[0124] The data of the specific resistance of each layer as obtainedaccording to the method mentioned above are as follows: NiFe has 20μΩcm; CoFe 13 μΩcm; spacer Cu 8 μΩcm; IrMn 250 μΩcm. If the underlayerof Ta (tantalum) is thick, its specific resistance will greatly varythrough crystallization. The cap Ta is much influenced by the surfaceoxides. Therefore, their accurate data could not be obtained. Thespecific resistance of the Ta layer is presumed to be 100 μΩcm. Based onthose data, the current flow ratio of each layer is obtained, and thecurrent magnetic field Hcu is calculated according to the formula (1-5).

[0125] The value of Hin is 25 Oe, as measured. Hpin is obtainedaccording to the formula (1-4).

[0126] In the film constitution of this case, the height is shortenedwhile the thickness of the pinned layer is thick. Therefore, the straymagnetic field, Hpin, from the pinned layer to the free layer is large.In addition, since more current flows above the free layer than belowit, the current magnetic field Hcu applied to the free layer is large.Accordingly, for designing the bias point, it may be employable tocontrol the bias point by canceling the large Hpin by the large currentmagnetic field Hcu.

[0127] The bias point values as calculated on the basis of the dataobtained above are shown in Table 1. The sense current is 4 mA. TABLE 1Calculated Bias Point in Film of Comparative Case 1 MR height[micrometers] Bias Point 0.3 70% 0.5 61% 0.7 53%

[0128] As is known from Table 1, the bias point falls between 61 and 70%when the MR height falls between 0.3 and 0.5 micrometers, and thisoversteps the calculated best bias point range.

[0129]FIG. 11 is a conceptual view showing the condition of the biaspoint in Comparative Case 1. It is understood that reducing the MRheight results in shifting of the bias point to the antiferromagneticsite (to the site larger than 50%). The MR height inevitably fluctuates,owing to the mechanical polishing. It is understood that the MR heightdistribution lowers the yield. Qualitatively, the reason is because thebias point is controlled in the extremely unstable method where thelarge pinned layer stray magnetic field Hpin is canceled by the largecurrent magnetic field Hcu.

[0130] Except for the bias point, the film of this Comparative Case hasstill another essential problem. The problem is that the ultra-thin freelayer to which the present invention is directed lowers the MR ratio.Through our experiments, we, the present inventors have found the factthat the MR ratio in the devices having a thinned free layer isextremely lowered after thermal treatment, and this is a serious problemwith the devices. For example, in the film constitution of ComparativeCase 1, the MR ratio in the as-deposited condition is around 11%, but is5.6% after thermal treatment. That is, the latter is about a half of theformer. In that condition, spin valve films practicable in high-densityrecording/reproducing systems could not be realized.

[0131] In the spin valve film of this Comparative Case, the layers areall thinned, and the sheet resistance of the film is around 30 Ω, and islarge. In view of the electrostatic discharge (ESD), the film is notpracticable. As well known, ESD increases with the increase in theresistance.

[0132] From the above, it is understood that the film of ComparativeCase 1 is not practicable at all in high-density recording heads.

[0133] Comparative Case 2: U.S. Pat. No. 5,422,591 (with Spin Filter butno Synthetic AF)

5 nanometer Ta/x nm Cu/1.5 nm NiFe/2.3 nm Cu/5 nm NiFe/11 nm FeMn/5nanometer Ta  (2)

[0134] In order to improve MR in the ultra-thin free layer therein, aspin valve film has been proposed, in which a high-conductivity layer islaminated on the free layer at the side opposite to the side of thenonmagnetic spacer layer. For example, referred to are U.S. Pat. Nos.2,637,360, 5,422,591 and 5,688,605.

[0135] The film (2) is an example of the spin valve film based on U.S.Pat. No. 5,422,591. In this spin valve film, the Cu layer adjacent tothe free layer at the side opposite to the side of the spacer Cu isthickened, whereby the mean free path for up-spin is prolonged toincrease the MR ratio. However, if the Cu layer is too much thickenedover the mean free path, it will be a simple shunt layer. Therefore, inthis film, the MR ratio peak appears at a certain Cu layer thickness.Based on this phenomenon, one problem with the film of Comparative Case1, that is, the reduction in the MR ratio owing to the ultra-thin freelayer could be overcome in some degree.

[0136] However, the film constitution of the spin valve film (2) basedon U.S. Pat. No. 5,422,591 has two problems. One is the problem with thebias point, and the other is the problem with the thermal stability forthe MR ratio.

[0137] First, regarding the viewpoint of the bias point, U.S. Pat. No.5,422,591 has no disclosure of direct description or indirectsuggestion. The constitution of the film (2) could not be used at all inpractical heads. The reasons are mentioned in detail hereunder.

[0138] In the same manner as in Comparative Case 1, the current magneticfield, Hcu, is obtained on the basis of the experimental data of thespecific resistance of each layer. In this case, the specific resistanceof Ta is presumed to be 100 μΩcm, and the experimental data of FeMn,NiFe, spacer Cu and subbing Cu are 250 μΩcm, 20 μΩcm, 8 μΩcm and 10μΩcm, respectively. The sense current is 4 mA. Though not described inU.S. Pat. No. 5,422,591, Hin has been found to fall between 15 Oe and 25Oe through our experiments. In this case, Hin is 20 oe.

[0139] The bias point is calculated for high-density recording heads forwhich the size of the device is as follows: track width=0.5 μm, MRheight=0.3 to 0.5 μm. The data are in Table 2.

[0140] Table 2

[0141] Calculated Bias Point in the Constitution of Comparative Case 2in which the subbing Cu thickness is varied MR height Cu (0 nm) Cu (1nm) Cu (2 nm) 0.3 μm 126% 143% 156% 0.5 μm 111% 127% 140%

[0142] In this constitution, the pinned layer stray magnetic field fromthe pinned layer to the free layer is extremely large, and the biaspoint is readily shifted to the plus side. As is known from the data ofthe bias point in Table 2, in the samples with no spin filter effect inwhich the subbing Cu thickness is zero, the bias point falls between111% and 126% at the MR height of from 0.3 to 0.5 μm. This means thatthe samples produce no output. This situation gets worse when thesubbing Cu layer thickness is thick as shown in table 2.

[0143]FIG. 12 is a conceptual view of the bias point versus Hin, Hpinand Hcu on a transfer curve. As Hpin is large, the bias point overstepsthe level when the current is zero. This constitution is so designedthat the bias point is forcedly reduced to 50% by means of an appliedcurrent magnetic field. In this constitution, however, since theunderlayer is a high-conductivity layer of Cu, I3 in FIG. 10 shall belarge and the current magnetic field, Hcu, to be obtained according tothe formula (1-5) shall be small. In other words, the bias pointcontrolling method is to cancel the large Hpin by the small Hcu that isopposite direction to Hpin, which is impossible to attain a good biaspoint value. It is further known from Table 2 that the increase in thesubbing Cu thickness results in further increase in the bias point.

[0144] Through our experiments mentioned above, we, the presentinventors have found that the bias point designing is quite difficult inthe constitution of U.S. Pat. No. 5,422,591, and that forming thehigh-conductivity Cu layer as the underlayer of the comparative casemakes the bias point more impracticable.

[0145] From the viewpoint of the thermal stability for the MR ratio, thefilm of U.S. Pat. No. 5,422,591 is not a practical one. As so describedin comparative case, the MR ratio in the as-deposited film surelyincreases owing to the spin filter effect. However, after the thermaltreatment for head fabrication, we, the present inventors have foundthat the MR ratio in the film of the comparative case is greatly reducedas the phenomenon peculiar to ultra-thin free films. This is a seriousproblem, if high output for high-density recording is intended.

[0146] In fact, the MR ratio in the as-deposited film of one example ofU.S. Pat. No. 5,422,591 (this is film (2)) is 1.8% when the subbing Cuthickness is 1 nanometer. However, after the thermal treatment in oursimulation, the MR ratio in the U.S. Pat. No. 5,422,591 lowered to 0.8%.As will be mentioned hereunder, the reason for the MR ratio reductionwill be essentially because of the antiferromagnetic film of FeMn inU.S. Pat. No. 5,422,591. Even if the ultra-thin free layer, with whichit is difficult to realize high MR, is used in the spin valve film so asto forcedly increase the MR ratio in the film owing to the spin filtereffect, the film will be quite useless in practical applications. It isunderstood from the data noted above that the simple spin filter effectcould not realize spin valve films having an ultra-thin free layer andexhibiting high MR ratio.

[0147] Comparative Case 3: JP-A 10-261209

5 nanometer Ta/3 nm Cu/1 nanometer Ta/5 nm NiFe/2.5 nm Cu/2.5 nm Co/10nm FeMn/5 nanometer Ta  (3)

[0148] In the film (3) disclosed in JP-A 10-261209, the Cu shunt layerdisposed adjacent to the free layer via Ta therebetween is, beingdifferent from the layer as intended for the spin filter effect for theMR ratio as in U.S. Pat. No. 5,422,591 of Comparative Case 2, intendedfor stabilizing the asymmetry by reducing the current magnetic field Hcuand by retarding the bias point fluctuation owing to sense current. Thisidea will be effective in the region where the free layer is relativelythick as in the film (3), but is quite ineffective in the case ofultra-thin free layers to which the present invention is directed, inview of the bias point and the MR ratio. Based on this idea, practicablefilms having an ultra-thin free layer could not be obtained at all. Thereasons are mentioned below.

[0149] First, regarding the bias point, when Hs is extremely reduced bythe use of the ultra-thin free layer, as in the film (2) of ComparativeCase 2, the best bias point could not be realized even though thecurrent magnetic field Hcu is reduced, if the pinned layer straymagnetic field is large. The advantage of the structure of the film (3)is that, when the free layer is thick, or that is, when Hs is relativelylarge, then the best bias point having been once obtained depends littleon the sense current. However, when the free layer in the filmconstitution of (3) is much reduced, it is naturally impossible torealize the best bias point. In other words, when the thickness of thefree layer in the film constitution of (3) is reduced to 4.5 nanometersor smaller so as to make the free layer applicable to high-densityrecording systems, the bias point shall be shifted to the plus side.

[0150] To verify the fact, the calculated bias point data of the filmconstitution are shown in Table 3. TABLE 3 Bias Point in Film ofComparative Case 3 MR height NiFe 5 nm NiFe 3 nm 0.3 μm 86% 108% 0.5 μm83% 104% 0.7 μm 81% 100%

[0151] Hin for the data calculation is 10 Oe. As in Table 3, it isunderstood that the bias point in the film constitution of ComparativeCase 3 is naturally shifted to the plus side even when the thickness ofthe NiFe film therein is 5 nanometers, and the film constitution is notwell designed. In this, the bias point is much more shifted to the plusside when the thickness of the free layer of NiFe is thinned to be 3nanometers.

[0152]FIG. 13 is a conceptual view showing the determinant factors forthe bias point in Comparative Case 3. As illustrated, since the currentmagnetic field Hcu only is reduced while Hpin is still large, no biaspoint is obtained at all in the region where the free layer is thick.Specifically, since the best bias point appears at the site where thetotal sum of the current magnetic field Hcu, the interlayer couplingmagnetic field Hin and the pinned layer stray magnetic field Hpin iszero, the film designing of such that the current center is made nearerto the free layer while only the current magnetic field is made zero, asin the constitution of (3), is quite meaningless.

[0153] The second problem with the constitution of (3) is that the film(3) could not have high MR ratio necessary for high-density recording.Specifically, in the constitution of (3), since a diffusion-preventinglayer of a material having a relatively high resistance is put betweenthe high-conductivity layer and the free layer, the film (3) could notenjoy the spin filter effect for MR, such as that in U.S. Pat. No.5,422,591 noted above, when the free layer is an ultra-thin one. In theregion where the free layer has a thickness of at most 4.5 nanometersand where the present invention is especially effective, as will bedescribed in detail hereunder, the film (3) will be useless as the MRratio therein is lowered.

[0154] For the two reasons mentioned above, the idea of the filmconstitution (3) is exclusively for the region where the free layer isrelatively thick, and it is understood that the idea is useless inpreparing practicable films having an ultra-thin free layer.

[0155] Comparative Case 4: Synthetic AF with No Spin Filter

5 nanometer Ta/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/7 nm IrMn/5 nanometer Ta  (4)

[0156] In this Comparative Case, employed is a Synthetic AF structurefor the purpose of improving the pinning characteristics. The twoferromagnetic layers are antiferromagnetically coupled to each other viaRu (ruthenium). One of the two ferromagnetic layers is pinned to theother via an antiferromagnetic layer existing therebetween. Even if theuni-directionally anisotropic magnetic field Hua is too small fornormally pinned structures, but if it is on a certain level, such asmall Hua is applicable to the Synthetic AF structure, and the pinningresistance of the Synthetic AF structure is high. As previouslymentioned hereinabove, in the Synthetic AF structure, the magnetizationdirections of the upper and lower ferromagnetic layers as coupled via Ruare opposite to each other, and the coupling magnetic field is severalkOe and is much larger than the medium magnetic field for headoperation. Approximately for the magnetic moment running outward,therefore, it is considered that the difference in Ms×t between theupper and lower pinned layer will be equal to the net moment.Specifically, it is possible to reduce the influence of the magneticfield strayed from the pinned layer to the free layer, and it isexpected that the reduction is advantageous for the bias point (see U.S.Pat. No. 5,465,185).

[0157] For example, in this Comparative Case, it is considered that thenet pinning thickness will be equivalent to the pinned layer having athickness of 0.5 nanometers, and it is possible to realize the pinnedlayer stray magnetic field equivalent to the thin pinned layer, which,however, could not be realized in normal pinning structures. Ideally,when the upper and lower pinned layers are controlled to have the sameproduct of Ms×t, then the pinned layer stray magnetic field could bezero. It has heretofore been considered that only the reduction in thepinned layer stray magnetic field will be satisfactory for good biaspoint designing for spin valve films for high-density recording. Thistime, however, we, the present inventors have found that, if only theSynthetic AF structure is employed, it is impossible to realize stablebias points in ultra-thin free layers applicable to high-densityrecording. The matters we have found are described in detail hereunder.

[0158]FIG. 14 is a conceptual view showing the determinant factors forthe bias point in this Comparative Case 4. Specifically, in theconstitution of this Comparative Case, the free layer is positioned,being much far from the current center of the current distribution inthe spin valve film. In this, therefore, the current magnetic filed Hcuis extremely large. Hin is at most 20 Oe or so, and the pinned layerstray magnetic field is extremely reduced owing to the Synthetic AFstructure employed. This means that the film constitution of thisComparative Case 4 is nearly in the just bias condition in the absenceof current. When current is applied to the spin valve film of thisconstitution, and when the applied current is increased, then the filmwill much overstep the just bias condition owing to the increasedcurrent magnetic field Hcu.

[0159] The calculated bias point data of this Comparative Case are shownin Table 4. TABLE 4 Calculated Bias Point Data of Film of ComparativeCase 4 MR height Hcu↑Hpin↑ Hcu↓Hpin↓ 0.3 μm 88% 22% 0.5 μm 80% 16% 0.7μm 73% 10%

[0160] Hin is 20 Oe. As so anticipated, it is understood from Table 4that the bias point could not fall the range of from 30 to 50%irrespective of the direction of the current flow.

[0161] For obtaining the just bias in this constitution, one means maybe taken into consideration, which comprises minimizing as much aspossible the pinned layer stray magnetic field, or that is, making theupper and lower pinned layers have the same thickness in the SyntheticAF structure thereby to make the pinned layer stray magnetic fieldnearly zero. It further comprises enlarging Hin as much as possible sothat the just bias could be in the current magnetic field for cancelingthe enlarged Hin. However, this means is undesirable. The enlarged Hinhas some negative influences on external magnetic field response. Theenlarged Hin shifts the linear region of the response and, in addition,reduces it. It will be good to control Hin to be small. However,fabricating spin valve films while the value is forcedly controlled tobe an unnaturally large and constant one is extremely difficult in massproduction and is unfavorable.

[0162] Since no high-conductivity layer is provided on the free layer atthe side opposite to the side of the spacer adjacent to the free layer,the MR ratio is lowered when the free layer is an ultra-thin one, forthe same reasons as in Comparative Case 1. Therefore, the filmconstitution of this Comparative Case 4 could not ensure satisfactoryoutput, when applied to high-density recording heads. This is theessential problem with this film constitution.

[0163] For the two reasons of bias point and high output mentionedabove, the spin valve film merely incorporating the Synthetic AFconstitution could not realize the use of ultra-thin free layers thereinfor high-density recording.

[0164] As has been described in detail hereinabove, we, the presentinventors have clarified, through many simulations in various currentmagnetic fields, that the film structures of Comparative Cases 1 to 4could not attain stable bias point and satisfactorily high output forspin valve films having an ultra-thin free layer for high-densityrecording. Through further studies and investigations, we have achievedthe present invention. The constitution of the invention is described indetail hereunder.

[0165]FIG. 15 is a graph of the free layer thickness dependence of thebias point in the spin valve films of the invention, as compared withthat in the spin valve films of the above-mentioned Comparative Cases.It is understood that the spin valve films of the Comparative Cases areall problematic in the bias point. The best bias point for spin valvefilms falls between 30 and 50%. For satisfactorily high sensitivity, thebias point must fall within the defined range at a low Ms×t free layer.

[0166] However, the bias point in the Comparative Cases significantlyoversteps the preferred range in the condition of low Ms×t. In addition,in the Comparative Cases, the bias point fluctuation relative to Ms×t isextremely large, and it is understood that the bias point is difficultto control in those Comparative Cases.

[0167] As opposed to the films of the Comparative Cases, it isunderstood that, in the film of Example 1 of the invention, the biaspoint fluctuation is extremely small relative to Ms×t, and the biaspoint is all the time within the preferred range.

[0168] In FIG. 15, the calculated bias point values in Comparative Case1 do not fall within the range between 30% and 50% even in the regionwhere Ms×t is not smaller than 5 nanometer Tesla. This is because, inthe actual region of low recording density for which a free layer havingMs×t of at least 5 nanometer Tesla is used, the MR height is large.Concretely, this is because the MR height for low recording densityheads is larger than the range of from 0.3 μm to 0.5 μm for the highrecording density to which the present invention is directed.

[0169] Anyhow, it is obvious that, in the region where Ms×t is at most 5nanometer Tesla, the bias point designing for the films of the inventionis much superior to that for the films of the Comparative Cases.

[0170]FIG. 16 is a graph of the MR ratio in the structures ofComparative Cases 1 to 4 with the product of Ms×t only in the free layerbeing reduced. In this, the MR ratio as plotted in the vertical axis isnearly proportional to the vertical axis of FIG. 9 for the transfercurve. For comparison, the data of Examples 1 and 2 of the invention tobe mentioned hereunder are also plotted in FIG. 16.

[0171] The film samples of Comparative Cases 1 to 4 and those of Example1 of the invention were prepared, in which the thickness of the freelayer of NiFe was varied for the varying Ms×t. The film samples ofExample 2 were prepared by varying the thickness of the free layer ofCoFe. All the samples were thermally annealed at 270° C. for 10 hours ina magnetic field of 7 kOe, and their data were measured.

[0172] In Comparative Case 2 and Examples 1 and 2, the high-conductivitylayer is of Cu, having a thickness of 2 nanometers. The points of Ms×tin the free layer as indicated by the arrows in FIG. 16 are for thefilms (1) to (4) of Comparative Cases mentioned above. For the Ms×t inthe free layer in all samples, Ms of NiFe is 1 T and Ms of CoFe is 1.8T. All the free layer thickness are expressed in terms of thickness withMs of 1 Tesla.

[0173] In the films of Comparative Cases 1, 3 and 4 where nohigh-conductivity layer is provided on the free layer, MR ratio isgreatly lowered with the reduction in Ms×t in the free layer. Thesefilms could hardly ensure high output capable of satisfying high-densityrecording.

[0174] In the film of Comparative Case 2 having a high-conductivitylayer, the free layer Ms×t dependence of the MR ratio is relativelysmall. However, since the antiferromagnetic layer in this film is ofFeMn, not containing a noble metal, the thermal stability for MR ratioin thermal treatment is low. With such small MR ratio, the film couldnot ensure high output for high-density recording.

[0175] In the films of Comparative Case 2 and Comparative Case 3, if alayer of Co or CoFe having a thickness of 0.5 nanometers is insertedbetween the spacer of Cu and the free layer of NiFe, the MR ratio willincrease by 1 to 2% above the data in the graph of FIG. 16. Even if so,however, the Ms×t dependence of the MR ratio is still the same as thatin the single-layer NiFe free layer. Anyhow, small MR ratio will do wellin the region where Ms×t in the free layer is small.

[0176] On the other hand, in the films of the invention where ahigh-conductivity layer is provided adjacent to the free layer and theantiferromagnetic layer contains a noble metal, the thermal stabilityfor the MR ratio after thermal treatment is good. The films of theinvention produce high output well applicable to high-density recording.In particular, the difference in the MR ratio between the films of theinvention and those of Comparative Cases is obvious in the region whereMs×t is smaller than 5 nanometer Tesla.

[0177] The magnetoresistance effect device of the invention is describedin detail hereunder.

[0178]FIG. 1 is a conceptual view showing the sectional constitution ofthe magnetoresistance effect device of the invention. As illustrated,the magnetoresistance effect device of the invention comprises ahigh-conductivity layer 101, a free layer 102, a spacer layer 103, afirst ferromagnetic layer 104, a coupling film 105, a secondferromagnetic layer 106 and an antiferromagnetic film 107, all laminatedin that order.

[0179] In the device with that constitution, the free layer 102 is muchthinned. On the transfer curve where Hs is small due to ultra thin freelayer, Hcu, Hpin and Hin are all small Hpin−Hin=Hcu, and a good biaspoint can be realized in the device. In general, in ultra-thin freelayers, high MR ratio is difficult to realize. The device of theinvention has overcome this problem. The device has good thermalstability for MR ratio, and therefore can realize high-output heads.

[0180] Specifically, even though having the ultra-thin free layer forhigh-density recording, the spin valve film constitution of theinvention can realize good bias point and can maintain high MR ratio.Therefore, the film stably produces high output. Concretely, in biaspoint designing, the condition of Hpin−Hin=Hcu is realized, and the filmhas good bias point. Reducing all Hpin, Hin and Hcu is important forstably realizing the condition of Hpin−Hin=Hcu.

[0181] Regarding Hpin, the film has a so-called Synthetic AF structurewhere the two ferromagnetic layers are antiferromagnetically coupled toeach other. In this, therefore, Hpin is derived from only the differencein the magnetic thickness between the two layers of the first and secondferromagnetic layers, and can be reduced.

[0182] From the formula (1-4), it is understood that reducing (Ms×t)pinin the pinned layer is effective for reducing Hpin.

[0183] However, for bias point designing in ultra-thin free layers, onlythe reduction in Hpin is meaningless. For this, the reduction in thecurrent magnetic field Hcu is indispensable. Therefore, the nonmagnetichigh-conductivity layer is provided on the free layer at the sideopposite to the side of the spacer layer, whereby the center of thecurrent distribution in the spin valve film can be near to the freelayer and Hcu can be thereby reduced. This is because, in the formulae(1-5) and (1-5-1), when I3 is increased for the top-type spin valve film(I₁ is increased for the bottom-type spin valve film) and the currentflow ratio C is lowered, then the current magnetic field Hcu can bereduced. Another significant function of the nonmagnetichigh-conductivity layer is to maintain high MR ratio in the ultra-thinfree layer, to which the invention is directed, owing to the spin filtereffect. Specifically, by providing the nonmagnetic high-conductivitylayer, the difference in the mean free path of up-spin can be kept largebetween the parallel condition and the antiparallel condition for themagnetization directions of the free layer and the pinned layer adjacentto the spacer.

[0184] For stably realizing the condition of Hpin−Hin=Hcu, the reductionin Hin is also important. For realizing the high MR ratio owing to thehigh-conductivity layer as provided adjacent to the ultra-thin freelayer (spin filter effect), it is important to thin the spacer. However,in general, Hin will increase with the reduction in the spacer thicknessand with the reduction in the free layer thickness. Overcoming thisproblem, it is important to use the device of the invention at Hinfalling within a range of from 0 to 20 Oe or so.

[0185]FIG. 2 is a schematic view of the transfer curve given by the spinvalve film of the invention. Even in the small transfer curve for whichthe ultra-thin free layer is used to give small Hs, all of Hpin, Hcu andHin are reduced, and it is possible to design the condition ofHpin−Hin=Hcu. Therefore, it is possible to settle the bias point in agood site of around 50% (good bias point around 40% in the valuecalculated by our method). In addition, since the film incorporates thehigh-conductivity layer exhibiting the spin filter effect, it stillmaintain high MR ratio even in the ultra-thin free layer. The value inthe vertical axis in FIG. 2 is satisfactorily high.

[0186] Next, the determinant factors for the bias point, namely theparameters of Hpin, Hin and Hcu are described in detail.

[0187] First, low Hcu is referred to. As previously describedhereinabove, the high-conductivity layer is provided on the free layerat the side opposite to the side of the spacer, whereby the value C inthe formula (1-5) is reduced and the current magnetic field Hcu isreduced. One concrete example of the film constitution is mentionedbelow.

5 nanometer Ta/x nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/7 nm IrMn/5 nanometer Ta

[0188]FIG. 3 is a graph of the Cu thickness of the high-conductivity Culayer adjacent to the free layer on the side opposite to the side atwhich the spacer is contacted with the free layer, versus the currentmagnetic field Hcu applied to the free layer. The sense current is 4 mA.As illustrated, the value C of the formula (1-5) becomes small with theincrease in the Cu film thickness, whereby the current magnetic fieldHcu is reduced. When the current flow ratio in the upper and lower sidesof the free layer is the same, the current magnetic field applied to thefree layer is always zero irrespective of the intensity of the sensecurrent applied thereto.

[0189] One key point of the invention is to reduce the current magneticfield. However, it is undesirable to make the current magnetic field Hcuzero. The invention satisfies the condition of Hpin−Hin=Hcu for biaspoint control. Therefore, designing the current magnetic field to reachzero, as in the Comparative Case 3 mentioned above, will make theintended bias point control impossible.

[0190] From the viewpoint of the current magnetic field, the suitablerange of the nonmagnetic high-conductivity Cu layer may fall a broadscope of from 0.5 nanometers to 4 nanometers. Since Hs is smaller withthe reduction in the free layer thickness, it is desirable that thecurrent magnetic field Hcu is smaller. In this Example, the nonmagnetichigh-conductivity layer is of Cu. Apart from this, when the layer is ofany other metal material or of a laminate film, it thickness could be interms of the thickness of the Cu layer. For example, where thenonmagnetic high-conductivity layer is a laminate film of 1.5 nm Ru/1 nmCu, the specific resistivity of Ru therein is 30 μΩcm and that of Cu is10 μΩcm, as measured through experiments. Therefore, the thickness ofthe laminate film will correspond to the Cu layer thickness of (1.5nm×10 μΩcm /30 μΩcm)+1 nm =1.5 nm.

[0191] In the same manner, for other metallic laminate films for thenonmagnetic high-conductivity layer, the current flow ratio could beobtained on the basis of the experimental data of specific resistivityof the constituent metals, 10 μΩcm for Cu, 30 μΩcm for Ru, 10 μΩcm forAu, 10 μΩcm for Ag, 20 μΩcm for Ir, 70 μΩcm for Re, 20 μΩcm for Rh, 40μΩcm for Pt, 40 μΩcm for Pd, 12 μΩcm for Al, and 3 0 μΩcm for Os. Wherethe nonmagnetic high-conductivity layer is of an alloy, its thicknesscould be also in terms of the Cu layer thickness, based on the specificresistance of the constituent elements as above, for which the specificresistance data may be proportionally partitioned according to theelemental composition.

[0192] As so mentioned hereinabove for the Comparative Cases, thespecific resistance of the metals constituting the nonmagnetichigh-conductivity layer will vary depending on the material with whichthe layer is contacted. However, the material to be contacted with thenonmagnetic high-conductivity layer does not differ so much in differentspin valve films. Therefore, the suitable range of the thickness of thenonmagnetic high-conductivity layer could be determined on the basis ofthe data of the specific resistance of the metals constituting thelayer.

[0193] As in the formula (1-5), Hcu depends on the current flow ratio ofthe upper and lower layers above and below the free layer. Therefore,for reducing Hcu, it is desirable that the thickness of the spacer layeras positioned at the side opposite to the side of the nonmagnetichigh-conductivity layer is as small as possible. This meets therequirement for the spin filter effect on MR ratio, which will bementioned hereunder. Concretely, it is desirable that the spacer filmthickness falls between 1.5 nanometers and 2.5 nanometers or so.

[0194] The nonmagnetic high-conductivity layer also functions as thelayer exhibiting the spin filter effect on MR ratio with the reductionin the current magnetic field Hcu. For its effect, the suitable range ofthe thickness of the layer will be limited in some degree. For example,where conductive electrons that move from the pinned layer to the freelayer are taken into consideration, it is desirable that the mean freepath for the electrons is large, depending on the magnetizationdirection of the free layer as to whether it is parallel or antiparallelto the magnetization direction of the pinned layer. Therefore, it isdesirable that the spacer film is thinner, not depending on spin-up orspin-down. To avoid increasing Hin, the preferred range of the spacerthickness falls between 1.5 nanometers and 2.5 nanometers.

[0195] It is also desirable that the free layer thickness is larger thanthe mean free path for down spin but is much smaller than that for upspin. For example, since the free mean path for down spin of NiFe isaround 1.1 nanometers, it is the best that the NiFe thickness fallsbetween 1 nanometers and 4.5 nanometers or so, and that the CoFethickness falls between 1 nanometers and 3 nanometers or so. The mostpreferred range of the high-conductivity layer thickness varies,depending on the pinned layer thickness, the spacer thickness and thefree layer thickness. With the spacer layer thickness being smaller, andwith the free layer thickness being smaller, the thickness of thehigh-conductivity layer for MR ratio peak is larger. For example, wherethe thickness of the pinned layer of CoFe is 2.5 nanometers, that of thespacer of Cu is 2 nanometers and that of the free layer of CoFe is 2nanometers, the high-conductivity layer of Cu having a thickness ofaround 2 nanometers gives MR ratio peak. In experiences, when the totalthickness of the free layer and the nonmagnetic high-conductivity layerof Cu falls between 4 and 5 nanometers or so, the high-conductivitylayer gives MR ratio peak. Therefore, it is desirable that the thicknessof the nonmagnetic high-conductivity layer is defined around the range.Where the nonmagnetic high-conductivity layer is of Cu, being adjacentto the free layer, the preferred range of the total thickness of the Culayer and the free layer falls between 3 nanometers and 5.5 nanometersor so including the margin.

[0196] Next referred to is Hpin. For reducing Hpin, it is desirable thatthe effective thickness of the pinned layer of CoFe with Bs being 1.8Tis at most around 2 nanometers (at most around 3.6 nanometers in termsof NiFe), more preferably at most 1.7 nanometer (at most 3 nanometers interms of NiFe), and most preferably at most 1 nanometer (at most 1.8nanometers in terms of NiFe). For realizing the preferred condition, itis desirable that the pinned layer has a Synthetic AF structure. Forexample, the structure is composed of antiferromagneticfilm/ferromagnetic film 1/0.9 nm Ru/ferromagnetic film 2, in which theferromagnetic film 1 is antiferromagnetically coupled to theferromagnetic film 2. One of the two ferromagnetic layer, theferromagnetic film 1 as antiferromagnetically coupled to the other ismagnetically pinned in one direction by the antiferromagnetic film. Themagnetization directions of the ferromagnetic film 1 and theferromagnetic film 2 are opposite to each other, and the couplingmagnetic field between them is several koe and is large. Therefore, asprimary approximation, it is considered that the difference between Ms×tof the ferromagnetic film 1 and that of the ferromagnetic film 2 wouldcontribute to the effective pinned layer stray magnetic field (U.S. Pat.No. 5,465,185).

[0197] For example, in the preferred constitution of IrMn/2 nm CoFe/0.9nm Ru/2.5 nm CoFe, the effective thickness of the pinned layer will be2.5 nanometers−2 nanometers=0.5 nanometers (the magnetic thickness willbe 0.9 nanometer Tesla) Reducing the effective pinned layer thickness,if possible, brings about the reduction in Hpin, as in the formula(1-4). When the pinned layer of low Mst is realized by normal pinnedstructure, it is able to obtain the good bias point without synthetic AFstructure.

[0198] Next referred to is Hin. From the viewpoint of the bias point andthe spin filter effect, it is desirable the thickness of the Cu layer asthe spacer is as small as possible, as so mentioned hereinabove.Concretely, it is desirable that, with such a thin spacer film, Hinfalls between 0 and 20 Oe or so, more preferably between 5 and 15 Oe orso. In the invention, one resolution for the film constitution notincreasing Hin even when the spacer is thin is a two-layered underlayerconstitution or the like.

[0199] Next referred to is the thermal stability for MR ratio. Whenultra-thin free layers are employed, it is extremely difficult tomaintain good thermal stability for MR ratio in thermal treatment.Concretely, two measures may be taken for improving the thermalstability for MR ratio of spin valve films incorporating an ultra-thinfree layer. One is to provide a nonmagnetic high-conductivity layer of acertain level, adjacent to the free layer. Needless-to-say, thenonmagnetic high-conductivity layer exhibits the spin filter effect. Inaddition, it has been found that the layer further acts to improve thethermal stability for MR ratio. It has been found that, though not sosignificant when the thickness of the neighboring free layer is around4.5 nanometers, the total thickness of the free layer and thenonmagnetic high-conductivity layer must be indispensably at least 1nanometer when the free layer is thinned to be around 2 nanometers. Forexample, when the nonmagnetic high-conductivity layer thickness is 0nanometer, the MR ratio after thermal treatment (at 270° C. for 10hours) will reduce by about 50% in terms of the relative ratio based onthe MR ratio in the as-deposited condition. However, if the nonmagnetichigh-conductivity layer of around 1 nanometer in thickness is provided,the MR ratio reduction is decreased to fall between 0 and 30%.

[0200] Even the first measure being taken, the thermal deterioration inMR ratio will still fluctuate. The second measure is to compensate forthis, for which the material for the antiferromagnetic film isspecifically defined. When the antiferromagnetic film is FeMn, thethermal deterioration is 30%. However, when it is IrMn, the thermaldeterioration could be reduced to 0 to 15%. The MR ratio in theas-deposited film in which is used antiferromagnetic PtMn could not bemeasured, but the MR ratio in the film after thermal treatment is equalto that in the as-deposited film with IrMn. Namely, the thermaldeterioration in MR ratio in the film with PtMn is almost 0%. Thethermal stability to MR ratio depends on the noble metal content of theantiferromagnetic film. It has been found that antiferromagnetic filmscontaining a noble metal, for example, those of IrMn, PtMn, PdPtMn orRuRhMn are especially preferred for the spin valve films of theinvention comprising an ultra-thin free layer.

[0201] Summarizing the above, FIG. 4 is a graph concretely showing therange of the pinned layer thickness and the nonmagnetichigh-conductivity layer thickness in Synthetic AF for realizingasymmetry of from -10% to +10%, or that is, for realizing bias points offrom 30% to 50% by our simplified calculation method. The “asymmetry” isdefined as (V1−V2)/(V1+V2), in which Vi indicates the peak value of thereproduction output in a positive signal field and V2 indicates the peakvalue of the reproduction output in a negative signal field. The“asymmetry of from −10% to +10%” corresponds to “(V1−V2)/(V1+V2) fallingbetween minus 0.1 and plus 0.1”.

[0202] For realizing Hpin−Hin=Hcu, Hcu must be lowered when Hpin issmall. In other words, as in the formulae (1-4) and (1-5), when thethickness of the upper and lower films of the pinned layer in SyntheticAF, (Ms×t)pin, is small, the thickness of the nonmagnetichigh-conductivity layer must be large; but, on the other hand, when(Ms×t)pin is large, the thickness of the nonmagnetic high-conductivitylayer must be small.

[0203] Concretely, the spin valve film with Synthetic AF of theinvention shall satisfy the conditions of 0.5nanometers≦tm(pin1)−tm(pin2)+t(HCL)≦4 nanometers and t(HCL)≧0.5nanometers, in which tm(pin1) indicates the thickness of the pined layerconstituting Synthetic AF, tm(pin2) indicates the thickness of theanother pinned layer constituting it, and t(HCL) indicates the thicknessof the nonmagnetic high-conductivity layer (in terms of the Cu layerhaving a specific resistance of 10 μΩcm). The condition of 0.5nanometers≦tm(pin1)−tm(pin2)+t(HCL) is for the limit for the bias pointof around 30%, or that is, for the asymmetry of +10%; and the conditionof tm(pin1)−tm(pin2)+t(HCL)≦4 nanometers is for the limit for the biaspoint of around 50%, or that is, for the asymmetry of −10%.

[0204] “tm(pin1)−tm(pin2)” indicates the magnetic thickness of thepinned layer in terms of NiFewithMs of 1 T. For example, in a SyntheticAF structure of PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe, the pinned layerthickness is (2.5−2)×1.8 T=0.9 nanometers. In the structureincorporating the single-layer pinned layer in the above-mentionedComparative Cases, used is Ms×t of the single-layer pinned layer.

[0205] t(HCL) indicates the thickness of the nonmagnetichigh-conductivity layer in terms of Cu. Where the nonmagnetichigh-conductivity layer is of any others except Cu, its thickness couldbe determined in terms of Cu, based on the above-mentioned data of thespecific resistance of the constituent component.

[0206] The condition of t(HCL)≧0.5 nanometers is to define the lowermostlimit of the thickness of the nonmagnetic high-conductivity layerindispensable for realizing high MR in the spin valve films in which thethickness of the free layer is smaller than 4.5 nanometers. Morepreferably, t(HCL)≧3 nanometers. This is because, when the thickness ofthe nonmagnetic high-conductivity layer is larger than 3 nanometers, ARswill lower. Also preferably, tm(pin1)−tm(pin2)≦3 nanometers. This isbecause, if the difference in the thickness between the upper and lowerfilms of the pinned layer in Synthetic AF is larger than 3 nanometers,the thermal stability for the pinned magnetization of the pinned layerwill lower.

[0207] In FIG. 4, plotted are the data of the Comparative Cases 1 to 4mentioned above and those of Example 1 to be mentioned in detailhereunder. In the Synthetic AF structure, where the magnetic thicknessof the pinned film adjacent to the spacer is larger than that of theother pinned film, the magnetic thickness of the pinned layer in thehorizontal axis is in the plus side in the graph of FIG. 4; and wherethe magnetic thickness of the pinned film adjacent to the spacer issmaller than that of the other pinned film, the magnetic thickness ofthe pinned layer in the horizontal axis is in the minus side. In theconventional pin layer constitution with no Synthetic AF, the magneticthickness of the pinned layer is all in the plus side.

[0208] As is known from FIG. 4, the films of the Comparative Cases areall outside the preferred range, or that is, their bias points are notgood and their asymmetry is large; but those of the invention all withinthe preferred range, or that is, their bias points are all good andtheir asymmetry is small.

[0209] Examples of concrete film structures of the invention arementioned below, in which the small Hpin in Synthetic AF is canceled bythe small Hcu to realize Hpin−Hin=Hcu through specific bias pointdesigning and the difficulties in improving the thermal stability for MRratio that is peculiar to ultra-thin free layer-incorporated spin valvefilms are overcome.

EXAMPLE 1 Top SFSV (with Free Layer of NiFe/Co(Fe))

5 nanometer Ta/x nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/ (2+y) nm CoFe/0.9nm Ru/2 nm CoFe/ 7 nm IrMn/5 nanometer Ta  (7-1)

[0210] This is to exemplify a so-called top-type spin valve film inwhich an antiferromagnetic layer is above a free layer.

[0211]FIG. 5 is a conceptual view showing a typical film constitution ofthe magnetoresistance effect device of this Example. Precisely, thedevice illustrated comprises a high-conductivity layer 101 peculiar tothe invention, a free layer 102 and a spacer layer 103 all laminated ona subbing buffer layer 112 in that order, and comprises pinnedferromagnetic layers 104 and 106 as antiferromagnetically coupled toeach other via a layer 105, in which the layer 106 is pinned in onedirection by an antiferromagnetic layer 107. On the antiferromagneticlayer 107, formed is a cap layer 113. In the film structure of (7-1),the free layer 102 is of a laminate film composed of two layers 110 and111, and the nonmagnetic high-conductivity layer 101 is a single layerof Cu.

[0212] The film (7-1) has achieved both good MR and good bias pointcontrol, owing to the MR spin filter effect of the subbing Cu layer andto the effect of the Synthetic AF structure to reduce Hpin. The biaspoint data for the film, as calculated according to the method mentionedabove, are in Table 5. TABLE 5 Calculated Bias Point Data MR height x =2 (a) y = 0.5, Hin = 20 Oe 0.3 μm 37% 0.5 μm 31% 0.7 μm 25% (b) y = 0.8,Hin = 20 Oe 0.3 μm 46% 0.5 μm 40% 0.7 μm 33% (c) y = 0.5, Hin = 10 Oe0.3 μm 42% 0.5 μm 39% 0.7 μm 36%

[0213] The subbing Cu layer has a thickness of 2 nanometers. In thestructure where the underlayer is a simple, single-layered,high-conductivity layer of Cu, Hin is 20 Oe and is relatively large. Inthat structure, it is known from the data of Table 5-(a) where thedifference in the thickness between the upper and lower pinned layers inthe Synthetic AF is 0.5 nanometers, that the bias points are shifted tothe minus side in some degree from the good bias point of 40% . The filmwith that structure is well practicable. The data of Table 5-(b) are forthe case of y=0.8 nanometers (Hpin is increased in some degree). In thestructure of this case, the bias point data are better than those in thestructure of (a) in which the bias point data are shifted lower. Thecase of (c) in which Hin is lowered also gives good bias point data.Comparing the data of (a), (b) and (c) in Table 5, it is obvious thatHin is preferably as small as possible. This is because of the reducedMR height dependence of the bias point. In the Synthetic AF structure,the smaller thickness difference between the upper and lower pinnedlayers gives smaller Hpin, thereby resulting in smaller MR heightdependence of the bias point. However, the difference of 0.3 nanometersbetween (a) and (b) could be negligible. Preferably, therefore, y=0 to 1nanometer (Ms×t =0 to 1.8 nanometer Tesla in NiFe), more preferably, y=0to 0.5 nanometers (Ms×t=0 to 0.9 nanometer Tesla in NiFe). Within thepreferred range, the value y is easy to control for obtaining good biaspoints and for improving other characteristics of the film including ESDresistance, etc.

[0214] The subbing Cu layer is for bias point control and for MR spinfilter effect. Increasing the subbing Cu thickness results in small Hcu,but also results in ARs reduction. Preferably, therefore, the Cuthickness falls between 0.5 nanometers and 4 nanometers, more preferablybetween 0.5 nanometers and 3 nanometers. The subbing Cu thickness enoughfor the MR spin filter effect depends on the constitution of the freelayer. With the free layer being thin, the most preferred thickness ofthe subbing Cu layer enough for the MR spin filter effect will shift toa larger value. In experiments, the peak of MR ratio appeared when thetotal thickness of the subbing Cu layer and the free layer fell between4 nanometers and 5 nanometers.

[0215] In the free layer constitution in (7-1) where the subbing Cuthickness is from 0 to 1.5 nanometers, the MR increase owing to the spinfilter effect of the increased Cu thickness will cancel the Rs reductionto be caused by the increase in the Cu thickness, and ΔRs changeslittle. In another where the subbing Cu thickness is from 1.5 nanometersto 2 nanometers, however, ΔRs will decrease by about 0.1 Ω; and in stillanother where the subbing Cu thickness is from 1.5 nanometers to 3nanometers, ΔRs will decrease by about 0.25 Ω. The ΔRs reduction shallbe nearly proportional to the output reduction, and is thereforeunfavorable. However, if thick subbing Cu is desired for bias pointcontrol, the subbing Cu thickness could be 3 nanometers in the freelayer constitution illustrated. In this case, since the current magneticfield per the unit current is small and since the spin valve filmresistance is lowered, the output reduction to be caused by the ΔRsreduction could be retarded by applying increased current. This isbecause the output is also proportional to the applied current. If ΔRshas decreased by 10% owing to the increase in the subbing Cu thickness,the calculated sense current of 4 mA maybe increased to 5 mA whereby theoutput will increase by 25%. In that manner, the output reduction causedby the ΔRs reduction could be well compensated for by the currentincrease.

[0216] For a thick free layer of 4 nm NiFe/0.5 nm CoFe, the subbing Cuthickness is preferably from 0.5 to 2 nanometers or so; but for a thinfree layer of 1 nm NiFe/0.5 nm CoFe, the subbing Cu thickness ispreferably from 1 to 4 nanometers or so. The thickness of the interlayerof CoFe may be varied within a range of from 0.3 to 1.5 nanometers. Inplace of CoFe, also employable is any of Co or other Co alloys. Where Cois used in place of CoFe, its thickness is preferably as small aspossible. This is because the Co single substance could not be softmagnetic by itself.

[0217] For example, when NiFe is 4 nanometers thick, then Co ispreferably from 0 to 1 nanometer thick; when NiFe is 2 nanometers thick,then Co is preferably from 0 to 0.5 nanometers thick; and when NiFe is 1nanometer thick, then Co is preferably from 0 to 0.3 nanometers thick.If the interfacial diffusion from the subbing Cu is desired to beprevented, a layer of a material not forming a solid solution with Cu,for example, Co or CoFe could be put between the subbing Cu layer andthe free layer. For example, the free layer may have a structure of 0.3nm Co/2 nm NiFe/0.5 nm Co, or 0.5 nm CoFe/2 nm NiFe/0.5 nm CoFe.

[0218] In place of the ultra-thin, laminated films of magnetic layers,an alloy free layer of NiFeCo may also be employed.

[0219] Ultra-thin free layers to which the invention is directed couldhardly realize low magnetostriction. One reason for the difficulty isthat the magnetostriction of NiFe becomes larger in positive when thethickness of the NiFe layer is smaller. In order to overcome theproblem, the NiFe composition could be Ni₈₀Fe₂₀ (at. %) in an ordinaryfree layer of 8 nm NiFe/1 nm CoFe. However, in the free layer of theinvention having a magnetic thickness of not larger than 4.5 nanometerTesla, it is desirable that the NiFe composition is an Ni-rich one overNi₈₀Fe₂₀. Concretely, for the NiFe film having a thickness of 4nanometers or so, desired is an Ni-rich composition over Ni₈₁Fe₁₉ (at.%); and for the NiFe film having a thickness of 3 nanometers or so,desired is an Ni-rich composition over Ni_(81.5)Fe_(18.5) (at. %). It isdesirable that the uppermost limit of the Ni content of NiFe is not overNi₉₀Fe₁₀ (at. %).

[0220] As mentioned above, the subbing Cu layer is to attain two majorobjects. One is to reduce the current magnetic field Hcu for good biaspoint control even in ultra-thin free layers; and the other is toexhibit the MR spin filter effect without lowering the MR ratio even inultra-thin free layers.

[0221] From the viewpoint of bias point control, the factors y and x inthe film (7-1) are determined in mutuality but not independently. Forexample, when y is smaller, then Hpin is also smaller. In this case, thecurrent magnetic field Hcu to cancel Hpin is preferably also smaller,and the value of x is preferably larger for the best results.

[0222] Concretely, one example of film thickness designing where thenonmagnetic high-conductivity layer is of Cu is as follows: When thepinned layer has 2 nanometer Tesla, the Cu layer thickness is from 0.5to 1.5 nm; when the pinned layer has 1.5 nanometer Tesla, the Cu layerthickness is from 1 to 2 nm; when the pinned layer has 1 nanometerTesla, the Cu layer thickness is from 1.5 to 2.5 nm; when the pinnedlayer has 0.5 nanometer Tesla, the Cu layer thickness is from 2 to 3 nm;and when the pinned layer has 0 nanometer Tesla, the Cu layer thicknessis from 2.5 to 3.5 nm.

[0223] Where the pinned layer is of Co or CoFe, its thickness shall bet=(Ms×t)pin/1.8 T [nanometer]; and where the pinned layer is of NiFe,its thickness shall be t =(Ms×t)pin/1 T [nanometer].

[0224] In the example 1, thickness of the pinned layer disposed to thespacer layer is larger than that of the another pinned layer, however itis possible that the pinned layer disposed on the spacer layer issmaller that that of the another pinned layer. In that case, thedirection of the current flow is opposite to the before case. In anotherwards, the direction of the Hpin and the Hcu should be always oppositeto each other.

[0225] In place of Cu, the spacer layer may be of any other element ofAu or Ag, or may be of an alloy comprising those elements. However, Cuis the best. For realizing high MR and for reducing as much as possiblethe thickness of the shunt layer that is on the free layer at the sideopposite to the side of the underlayer to thereby reduce the currentmagnetic field, it is desirable that the spacer thickness is as small aspossible. However, if the spacer is too small, the ferromagneticcoupling between the pinned layer and the free layer will increase toenlarge Hin. Preferably, therefore, the spacer thickness falls between1.5 nanometers and 2.5 nanometers, more preferably between 1.8nanometers and 2.3 nanometers.

[0226] The subbing high-conductivity layer to fill the significant rolesof the spin filter effect and the current magnetic field reduction isherein a single layer of Cu. The layer may also be of a laminate film.In the top-type spin valve film, the layer acts also as an fcc seedlayer. Therefore, the material of the underlayer is preferably an fcc orhcp metal material. Concretely, the layer may be an alloy layer ofmetals of Au, Ag, Al, Zr, Ru, Rh, Re, Ir, Pt, etc.; or it may be of alaminate layer of those metals. For only the MR spin filter effect andthe current magnetic field reduction, the simple Cu underlayer will besatisfactory. The alloy layer or the laminate film for the underlayerhas additional two effects; one for magnetostriction control inultra-thin free layers and the other for Hin control therein.Concretely, the following example is mentioned.

5 nanometer Ta/1 nm Ru/1.5 nm Cu/2 nm NiFe/0.5 nm CoFe/ 2 nm Cu/2.5 nmCoFe/0.9 nm Ru/2 nm CoFe/7 nm IrMn/5 nanometer Ta  (7-2)

[0227] With the Ru underlayer of 1 nanometer thick, the film smoothnessis improved, and with the spacer of 2 nanometers thick, Ms×t of the freelayer could be 2.9 nanometer Tesla in terms of NiFe. Thus, even thoughthe free layer is an ultra-thin layer, it readily realizes low Hin ofaround 10 Oe. Such low Hin is desirable, as the MR height dependence ofthe bias point is reduced. In addition, it is also desirable, as capableof realizing good bias point control even in the absence of anycomplicated thickness difference between the upper and lower pinnedlayers in the Synthetic AF. In the illustrated case (7-2), the Ruthickness is 1 nanometer, but is preferably from 0.5 nanometers to 5nanometers, more preferably from 1 nanometers to 3 nanometers or so. Thepreferred thickness range could apply to other materials except Ru.

[0228] In the film (7-2), Hcu corresponds to the sum of the electricalshunt layers of Ru and Cu. For example, for Ru, its specific resistanceis 30 μΩcm and is about 3 times that of Cu. From the viewpoint of Hcu,the film (7-2) shall be equivalent to a film having a Cu thickness of1.8 nanometers. However, from the viewpoint of MR, the resistance of Ruis high and shortens the mean free path for electrons. Therefore, if Ruis directly contacted with NiFe, the film structure could not almostexhibit a spin filter effect. Therefore, it is desirable that the layerto be contacted with the free layer is of a low-resistance material suchas Cu, Au, Ag of the like. For Ru, it is desirable that it is contactedwith the free layer via Cu, Au, Ag or the like in the form of atwo-layered film. This is one reason why the underlayer is of atwo-layered film.

[0229] In the illustrated case, the buffer layer of Ta is used. However,if the high conductance layer could exhibit the buffer effect by itself,the Ta layer will be not needed. For example, when a Zr layer is used inplace of Ru, the Ta layer may be omitted.

[0230] For the buffer layer, any of Ti, Zr, W, Cu, Hf, Mo or theiralloys may be employed in place of Ta. The thickness of the buffer layermade of any of them preferably falls between 1 nanometer and 7nanometers, more preferably 2 nanometers and 5 nanometers or so.

[0231] In the illustrated case, the AF film is of IrMn (Ir: 5 to 40 at.%). The IrMn film thickness preferably falls between 3 nanometers and 13nanometers or so. The merits of IrMn are that, since the IrMn film couldexhibit good pinning capabilities even though thin, it is suitable tonarrow gap heads for high-density recording, and that, as containing thenoble metal, it could maintain high MR ratio even after thermaltreatment. The antiferromagnetic film of FeMn as in Comparative Case 2could not maintain high MR ratio after thermal treatment. The demerit ofthe antiferromagnetic film of FeMn is especially remarkable inultra-thin free layers such as those in the invention.

[0232] As the antiferromagnetic film, also employable is any of CrMn,NiMn and NiO. However, for realizing high MR ratio, AF films containinga noble metal are preferred. For example, in place of Ir, employable isPd, Rh or the like. As compared with FeMn and NiMn films, the noblemetal-containing AF films are more effective for improving MR ratio, andtherefore could maintain high MR ratio even after annealing thermaltreatment that is indispensable to heads. Still another preferredexample of the materials for AF films is PtMn of which the noble metalcontent is much higher.

5 nanometer Ta/x nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nmRu/2 nm CoFe/10 nm PtMn/5 nanometer Ta  (7-3)

5 nanometer Ta/x nm Ru/y nm Cu/2 nm NiFe/0.5 nm CoFe/2 nm Cu/2.5 nmCoFe/0.9 nm Ru/2 nm CoFe/10 nm Ptmn/5 nanometer Ta  (7-4)

[0233] Using PtMn (Pt: 40 to 65 at. %) is advantageous in that, sincethe noble metal content of this is much higher than that of IrMn notedabove, the MR degradation in annealing is much lower and therefore highMR ratio could be realized to enlarge ΔRs, whereby the output could beincreased. In the spin valve film having an ultra-thin free layer whichcan hardly realize good thermal stability for MR, most preferred for thebest thermal stability for MR is a combination of a subbing Cu layerwith a spin filter effect and a layer of PtMn. In place of PtMn, alsoemployable is PdMn or PdPtMn (noble metal content: 40 to 65 at. %).

[0234] From the viewpoint of thermal stability for MR, it is desirablethat the subbing Cu layer has a thickness of at least 1 nanometer. Thisis because, if the thickness of the Cu layer is smaller than 1nanometer, the thermal stability for MR will be poor. However, when thethickness of the NiFe layer is not smaller than 4 nanometers, the Culayer may well be 0.5 nanometers thick for good thermal stability forMR.

[0235] The specific electric resistance of PtMn is large and is nearlythe same as that of IrMn. Therefore, PtMn is favorable, as having littleinfluence on the current magnetic field. For those reasons, the films(7-3) ad (7-4) are extremely favorable to practical applications.

[0236] However, one demerit of PtMn is that, since its criticalthickness for producing a unidirectional anisotropic magnetic field islarger than the critical thickness of IrMn, it is difficult to thin thePtMn film to 5 nanometers or so. Therefore, when PtMn is used, it isdesirable that the thickness of its film falls between 5 nanometers and30 nanometers, more preferably between 7 nanometers and 15 nanometers orso. The same idea as in (7-4) where the underlayer below the free layerhas a two-layered structure could apply also to PtMn.

[0237] As variations of the embodiments (7-1) to (7-4), a noble metalelement film could be laminated on the antiferromagnetic film. Forexample, a single-layered or laminated film of any of Cu, Ru, Pt, Au,Ag, Re, Rh, Pd and the like may be used. The variations could realizelow Hin even when the spacer is thin. However, if the noble metal filmis too thick, the current flow ratio will increase in the upper layersover the free layer. Therefore, the thickness of the single-layered orlaminated film preferably falls between 0.5 nanometers and 3 nanometersor so.

[0238] As has been mentioned hereinabove with reference to FIG. 15, thebias point control in the spin valve films of this Example is muchbetter than that in those of Comparative Cases 1 to 4, and the films ofthis Example could ensure the best bias points.

[0239] As also mentioned with reference to FIG. 16, the spin valve filmsof this Example produce higher MR ratio than that to be produced by thefilms of Comparative Cases 1 to 4 essentially bellow 45 nanometer Teslafree layer.

EXAMPLE 2 Top SFSV (with Simple CoFe Free Layer)

5 nanometer Ta/x nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/7 nm IrMn/5 nanometer Ta  (8-1)

5 nanometer Ta/x nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2 nmCoFe/10 nm PtMn/5 nanometer Ta  (8-2)

[0240] In this Example 2, used is a simple free layer of a single-layerCoFe, being different from the laminate free layer of NiFe/Co orNiFe/CoFe as in Example 1. In FIG. 1, the structure of this Example 1has a single-layer CoFe as the free layer 102 and a single-layer Cu asthe high-conductivity layer 101.

[0241] As already mentioned ultra-thin free layers below 4.5 nanometerTesla in NiFe face various difficulties. The single-layer CoFe freelayer is advantageous in that the soft magnetic characteristics controlis relatively easy even though the thickness of the layer is extremelysmall. A third additive element of B, Cu, Al, Rh, Pd, Ag, Ir, Au, Pt,Ru, Re, Os or the like could be added to CoFe, if desired. However, ifpure Co is used in place of such CoFe alloys, soft magneticcharacteristics characteristics could not be realized. CoFe preferablyfalls between Co₈₅Fe₁₅ (at. %) and Co₉₆Fe₄ (at. %). As will be mentionedhereunder, the defined composition range for CoFe is based on themagnetostriction control.

[0242] From the view point of soft magnetic characteristics, the CoFefree layer is preferably oriented in fcc(111). From the viewpoint ofbetter spin filter effect, the layer is preferably oriented in fcc(111)so as to reduce the resistance. However, a microcrystalline or amorphousfree layer of CoFeB is also employable.

[0243] Ms of the simple CoFe free layer is larger than that of NiFe.Therefore, for realizing the same degree of Ms×t, the CoFe layer couldbe thinner than the NiFe layer. From the viewpoint of the spin filtereffect, the simple CoFe free layer is preferred. For example, forrealizing a free layer of 4.5 nanometer Tesla, NiFe/CoFe must be 3.6 nmNiFe/0.5 nm CoFe, and its total thickness is about 4 nanometers. Asopposed to this, the thickness of the simple CoFe free layer could be2.5 nanometers. The latter is thinner by about 1.5 nanometers than theformer, NiFe/CoFe. Where a high-conductivity layer is provided below thefree layer of the two films, the down spin electrons will be filteredout, since they are thick as compared with the mean free path for downspin of about 1 nanometer. However, at a total thickness of around 4nanometers of NiFe/CoFe, the mean free path for down spin will be nearto that for up spin. In that condition, the underlying high-conductivitylayer will produce a simple shunt effect. Therefore, increasing thehigh-conductivity layer thickness causes MR reduction owing to the shunteffect.

[0244] On the other hand, for the simple CoFe, the mean free path of upspin is longer than 2.5 nanometers. Therefore, providing ahigh-conductivity layer of which the thickness is not so large willresults in the increase in the mean free path for up spin, therebyincreasing MR. In experiences and through experiments, it is known that,where Cu is used for the high-conductivity layer, MR peaks appear whenthe total thickness of the Cu layer and the free layer of NiFe/CoFe orCoFe is 4 nanometers or so, or falls between 3 nanometers and 5nanometers. In other words, when the high-conductivity layer that isnecessary for bias point designing is relatively thick, NiFe/CoFe rathercauses MR reduction owing to the shunt effect but not to the spin filtereffect, while, on the other hand, CoFe satisfies both good bias pointcontrol and MR increase owing to the spin filter effect. Therefore, CoFeis advantageous. This is because, as so mentioned hereinabove, the MRpeaks depend on the total thickness of the high-conductivity layer andthe free layer. Therefore, when the CoFe layer thickness is smaller,then the Cu layer thickness to give MR peaks shall be larger, and thespin filter effect and the bias point control both could be augmented.For the reasons mentioned above, the simple CoFe free layer is preferredfor spin valve films.

[0245] The thermal stability for MR of the laminated NiFe/CoFe freelayer is worse than that of the simple CoFe free layer, and the simpleCoFe free layer is better, as producing large MR.

[0246] The simple CoFe free layer is still better than the ultra-thin,laminated NiFe/CoFe layer, as its magnetostriction control is easy. Inparticular, the interfacial magnetostriction is important in ultra-thinfree layers. Therefore, NiFe/CoFe is inferior to simple CoFe, as theformer shall have one additional interface.

[0247] The bias point in the constitution of (8-1) could fall within agood range of from 30 to 50% or so, as in Example 1. Also like inExample 1, the MR height dependence of the free layer in (8-1) is small.

[0248] Regarding the Ms×t dependence of the free layer, smaller Ms×tgives smaller saturation magnetization Hs on the transfer curve, andrequires severer bias point control. Concretely, much reducing thecurrent magnetic field is important, and increasing thehigh-conductivity layer thickness is needed. As previously mentionedhereinabove, in the spin valve films of the invention, the thickness ofthe high-conductivity layer capable of producing MR peaks owing to thespin filter effect shall be larger with the reduction in the thicknessof the free layer. This well matches with the constitution of thisExample. It is understood that the idea of designing the spin valvefilms of the invention is favorable to heads for high-density recording.

[0249] Concretely, when Ms×t of the free layer is 4.5 nanometer Teslaand the thickness of the CoFe film is 2.5 nanometers, then the preferredrange of the high-conductivity film thickness falls between 0.5nanometers and 4 nanometers or so, more preferably between 0.5 nanometerand 3 nanometers or so in terms of the 10 microohm centimeter Cu; whenMs×t of the free layer is 3.6 nanometer Tesla and the thickness of theCoFe film is 2 nanometers, then the preferred range of thehigh-conductivity film thickness falls between 0.5 nanometer and 4nanometers or so, more preferably between 1 nanometers and 3.5nanometers or so in terms of Cu; when Ms×t of the free layer is 2.7nanometer Tesla and the thickness of the CoFe film is 1.5 nanometers,then the preferred range of the high-conductivity film thickness fallsbetween 0.5 nanometers and 4 nanometers or so, more preferably between 2nanometers and 4.5 nanometers or so in terms of Cu; and when Ms×t of thefree layer is 1.8 nanometer Tesla and the thickness of the CoFe film is1 nanometer, then the preferred range of the high-conductivity filmthickness falls between 0.5 nanometers and 4 nanometers or so, morepreferably between 2 nanometers and 4 nanometers or so in terms of Cu.

[0250] In (8-1) IrMn is used as the antiferromagnetic film; while in(8-2), PtMn is used as the same. Using PtMn is more advantageous in thatthe thermal stability for MR is much more improved and the output ismuch more increased. This is the same as in the case of the NiFe/Co(Fe)free layer. However, PtMn is problematic in that Hin will readilyincrease. Therefore, for good bias point control, either the measure ofmore reducing the current magnetic field Hcu or the measure of moreincreasing Hpin will be needed for PtMn than for IrMn. For reducing Hcu,σt in the high-conductivity layer may be increased, or that is, thethickness of the high-conductivity layer may be increased. Because oflarge Hin, the difference in the thickness between the upper and lowerpinned layer in the Synthetic AF may be increased more for PtMn than forIrMn. However, increasing the thickness of the high-conductivity layerwill cause the reduction in ΔRs. Therefore, as compared with that forIrMn, it is desirable that the thickness of the high-conductivity layermay be controlled to fall between 0.5 and 3 nanometers or so in terms ofCu for PtMn. As previously mentioned herein, increasing Δt in theSynthetic AF structure is unfavorable since it increases the MR heightdependence of the bias point. Therefore, as compared with that for IrMn,it is desirable that the intrinsic thickness of the pinned layer may beincreased by from 0 to 1 nanometer or so in terms of CoFe for PtMn. Thefollowing variations of (8-1) and (8-2) are within the scope of theinvention.

5 nanometer Ta/x nm Ru/y nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2nm CoFe/7 nm IrMn/5 nanometer Ta  (8-3)

5 nanometer Ta/x nm Ru/y nm Cu/2 nm CoFe/2 nm Cu/2.5 nm CoFe/0.9 nm Ru/2nm CoFe/10 nm PtMn/5 nanometer Ta  (8-4)

[0251] In those variations, the high-conductivity layer is of a laminatefilm of Ru/Cu but not a single-layer Cu. The reasons for the laminatefilm are the following two.

[0252] 1. CoFe magnetostriction control.

[0253] 2. Hin reduction.

[0254] The CoFe magnetostriction control of 1 is to control themagnetostriction of CoFe through the distortion control of itself, aswill be mentioned hereunder. Specifically, the fcc-d(111) spacing inCoFe is enlarged more than the that on simple Cu, high conductivitylayer magnetostriction in the CoFe free layer is controlled to be nearlyzero. The magnetostriction of Co₉₀Fe₁₀ (at. %) is often enlarged in thenegative side in an ordinary condition. Therefore, the material to bebelow the Cu layer preferably has a large atomic radius than Cu. Forexample, Ru is preferred. In addition to this, also preferred are Re,Au, Ag, Al, Pt, Rh, Ir, Pd, etc. For the magnetostriction control, theunderlayer is made to have a two-layered structure, or the CoFecomposition may be varied from 90-10 at. % to any others. Concretely,employable are CoFe alloy free layers having a varying composition offrom Co₉₀Fe₁₀ to Co₉₆Fe₄.

[0255] The Hin reduction of 2 is because Ru has the ability to planarizethe growing film. As previously mentioned hereinabove, Hin is preferablyas small as possible for good bias point designing based on Hcu andHpin. In particular, the spacer thickness is preferably as small aspossible in two points of the MR spin filter effect and the shuntreduction in the upper free layer. For this, needed is a technique ofusing an ultra-thin spacer of Cu having a low Hin. In the constitutionhaving a laminate Ru/Cu film, where the underlayer is of 1.5 nm Ru/1 to2 nm Cu, the free layer of CoFe is an ultra-thin free layer having Ms×tof 3.6 nm and a thickness of 2 nanometers, and the spacer Cu has athickness of 2 nanometers, Hin could be from 7 to 13 Oe or is low.Considering the fact thatHin in the embodiments of (7-1) and (7-2) isaround 20 Oe, the Hin reduction in the embodiments (8-3) and (8-4) issignificant.

[0256] For Hcu calculation, σt shall be obtained from the specificresistance of Ru in terms of Cu having 10 microohm centimeter. Thespecific resistance of Ru as obtained in experiments is 30 μΩcm. For theshunt effect, the thickness of Ru could be ⅓ of that of Cu having aspecific resistance of 10 μΩcm. For example, the shunt in theconstitution of 1.5 nm Ru/1 nm Cu could be equivalent to that in Cu of(1.5 nanometers/3)+1 nanometer=1.5 nanometer in thickness.

[0257] In variations of the embodiments (8-1) to (8-4), a noble metalelement film may be further laminated over the antiferromagnetic film.For example, employable is any of a single-layered or laminated films ofCu, Ru, Pt, Au, Ag, Re, Rh, Pd, etc. In those constitutions, low Hincould be realized even when the spacer film therein is thin. However, ifthe laminated film is too thin, the current flow ratio will be large inthe upper free layer. Therefore, the thickness of the single-layered orlaminated film preferably falls between 0.5 nanometers and 3 nanometersor so.

EXAMPLE 3 Bottom SFSV (with NiFe/Co(Fe) Free Layer)

5 nanometer Ta/2 nm Ru/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/0.5 nm Co/2 nm NiFe/2 nm Cu/5 nanometer Ta  (9-1)

5 nanometer Ta/1 nm Ru/2 nm NiFeCr/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nmCoFe/2 nm Cu/0.5 nm Co/2 nm NiFe/2 nm Cu/5 nanometer Ta  (9-2)

[0258] This is to exemplify a so-called bottom-type spin valve film inwhich an antiferromagnetic layer is below a free layer. FIG. 6 is aconceptual view showing the spin valve film constitution of thisExample. Precisely, the film illustrated comprises an antiferromagneticfilm crystallization control layer 128 and an antiferromagnetic film 127as laminated on a subbing buffer layer 131, and comprises pinned layers126 and 124 as antiferromagnetically coupled to each other via a layer125. On the layer 124, laminated are a spacer layer 123, a free layer122 and a nonmagnetic high-conductivity layer 121 in that order. Finallyprovided is a cap layer 132 over them.

[0259] In the embodiment of (9-1), the antiferromagnetic filmcrystallization control layer 128 is a single layer of Ru, theantiferromagnetic film 127 is of PtMn, and the free layer 122 is of alaminate film composed of two layers 129 and 130. In the embodiment of(9-2), the antiferromagnetic film crystallization control layer 128 is atwo-layered film composed of a film 133 of Ru and a film 134 of NiFeCr,the antiferromagnetic film 127 is of IrMn, and the free layer 122 is ofa two-layered film composed of two layers 129 and 130.

[0260] In the bottom-type spin valve film, the antiferromagnetic filmcrystallization control layer is provided over the buffer layer of Ta orthe like, and it is a subbing film of fcc or hcp having a thickness offrom 1 nanometer to 5 nanometers or so. For example, employed are alloyfilms or laminate films of Cu, Au, Ru, Pt, Rh, Ag, Ni, NiFe, etc. Theseed layer is important for increasing the function of theantiferromagnetic film. In the embodiment of (9-1) incorporating PtMn,used is a single-layered Ru layer; while in (9-2) incorporating IrMn,used is a laminate film of Ru/NiFeCr. In the constitution with theantiferromagnetic film crystallization control layer of that type, theblocking temperature for the antiferromagnetic film could be elevated toa satisfactorily high level, the film planarization could be promoted,and low Hin could be realized even for the ultra-thin spacers of from1.5 to 2.5 nanometers thick or so that are needed in the invention.

[0261] The bias point control to be effected in the invention is not somuch influenced by the type of the seed layer when the thickness of theseed layer falls within the range defined in this Example. However, lowresistance materials having a small specific resistance are unfavorableto the seed layer. This is because, if the shunt current flow isincreased in the layer, it would be difficult to make the current centernear to the free layer. Therefore, for the seed layer, it is desirableto use materials having as high as possible resistance and capable ofenhancing the function of the antiferromagnetic film. For example, inplace of using low-resistance NiFe alone, any of Cr, N, Hf, W, Ta andthe like may be added to NiFe so as to increase the specific resistanceof the NiFe layer. In (9-2), used is NiFeCr in place of NiFe.

[0262] As the antiferromagnetic film, used is PtMn in (9-1), and IrMn in(9-2). PtMn is advantageous in that the blocking temperature is high,that Hu.a. is large, and that the thermal stability for MR is loweredlittle after thermal treatment. With PtMn being used, therefore, high MRand high ARs could be realized. Like in the top-type structure, themerit of the noble metal-containing antiferromagnetic film of PtMn inthe bottom-type structure is significant in that high MR could bemaintained still after thermal treatment and even when ultra-thin freelayers are used. In place of PtMn, PdPtMn is also employable. Thepreferred thickness range of the layer falls between 5 nanometers and 30nanometers, more preferably between 7 nanometers and 15 nanometers.

[0263] The merit of IrMn in (9-2) is that it can maintain itscharacteristics even when its thickness is smaller than the thickness ofPtMn. Therefore, IrMn is suitable to narrow-gap heads for high-densityrecording. Preferably, the IrMn thickness falls between 3 nanometers and13 nanometers. The IrMn film is also an antiferromagnetic filmcontaining the noble metal Ir, and its thermal stability for good MRratio is excellent. In place of IrMn, also employable is noblemetal-containing RuRhMn.

[0264] As mentioned above, PtMn, IrMn and PdPtMn are the best for theantiferromagnetic film. However, the bias point control in the spinvalve films of the invention is not limited by the material of theantiferromagnetic film. In the invention, also employable are any otherantiferromagnetic films of NiO, CrMnPt, NiMn, α-Fe₂O₃, etc.

[0265] As the ferromagnetic material for the two pinned layer in theSynthetic AF structure, herein used is an CoFe alloy. In place of this,also employable are Co, NiFe and even laminate films of NiFe with Co orCoFe. Regarding the constituent materials and the film thicknesses, thesame as in the top-type structures of Examples 1 and 2 noted above couldapply to the bottom-type structure herein. The most significant objectof the Synthetic pinned layer structure, which is the key point in theinvention, is to reduce the pinned stray magnetic filed, as so mentionedhereinabove. The difference in Ms×t between the upper and lowerferromagnetic layers shall be closely related to the thickness of thehigh-conductivity layer as provided adjacent to the free layer.

[0266] Regarding the spacer, the same idea as that for the top-typestructure shall apply also to the bottom-type structure. Also in thebottom-type structure, the spacer layer is as thin as possible.Concretely, the spacer thickness preferably falls between 1.5 nanometersand 2.5 nanometers, more preferably between 1.8 nanometers and 2.3nanometers.

[0267] In this Example, the free layer is of a laminate film of NiFe/Co.Regarding the thickness and the material of the free layer, the same asin the top-type structure shall apply to the bottom-type structure.However, the NiFe composition for the subbing film differs between thetop-type structure and the bottom-type structure, and the preferred NiFecomposition for realizing low magnetostriction in the bottom-typestructure differs in some degree from that in the top-type structure.Concretely, in the case of a laminated free layer of NiFe/CoFe, thepositive side shifting of the magnetostriction in the laminatedNiFe/CoFe free layer to be caused by the reduction in the thickness ofNiFe in the bottom-type structure is smaller than that in the top-typestructure. Therefore, in the bottom-type structure, Ni-poorer NiFecompositions could well realize the reduction in the magnetostrictionthan in the top-type structure.

[0268] For example, in the case of a laminated free layer of 3 nmNiFe/0.5 nm CoFe, the NiFe composition of Ni₈₁Fe₁₉ (at. %) is notapplicable to the top-type structure as the magnetostriction in thepositive side is large, but is applicable to the bottom-type structureas the magnetostriction in the positive side is satisfactorily small inpractical applications.

[0269] The high-conductivity layer is the second significant key pointin the invention the same as the top type spin valve as mentionedbefore. In this Example, the high-conductivity layer is of a Cu film.The most significant role of the high-conductivity film is to make thecurrent center near the free layer as much as possible thereby reducethe current magnetic field.

[0270] Still another role of the film is to exhibit the spin filtereffect for MR owing to the conductivity of Cu. Therefore, even throughthe ultra-thin free layer is employed herein, the MR ratio degradationis small.

[0271] Regarding the optimum thickness range of the Cu layer, the sameas in invention of the top type spin-valve may apply also to the bottomspin-valve of this Example. Like in the top-type structure, the optimumthickness range of the Cu layer varies also in bottom-type structure,depending on the thickness of the free layer, and on the difference inthe thickness between the upper and lower pinned layers of the SyntheticAF. In addition to its role for bias point control and for high MR ratioretention, still another important role of the Cu cap layer is torealize low Hin in ultra-thin free layers. For example, when Hin in afree layer is 30 Oe or more in the absence of the Cu cap layer, it couldbe reduced to about 10 Oe in the same free layer in the presence of theCu cap layer.

[0272] In variations of (9-1) and (9-2), the high-conductivity layer maybe of a laminate film composed of at least two layers, in place of thesingle-layer high-conductivity layer of Cu as disposed adjacent to thefree layer of CoFe. For example, the laminate film for thehigh-conductivity layer may include Cu/Ru, Cu/Re, Cu/Rh, Cu/Pt, etc. Theessential object of the two-layered high-conductivity layer is tocontrol the magnetostriction Xs in the free layer. This is because, asso mentioned hereinabove for the top-type structure, themagnetostriction in the free layer of CoFe is influenced by thedistortion of the free layer itself. Moreover reduction in Hin isimportant in the invention. For reducing Hin, the two-layeredhigh-conductivity layer will be effective.

[0273] Embodiments of the variations are mentioned below.

5 nanometer Ta/2 nm Ru/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2nmCu/0.5 nmCo/2 nmNiFe/1.5 nmCu/1.5 nmRu/5 nanometer Ta  (9-3)

5 nanometer Ta/1 nm Ru/1 nm NiFeCr/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nmCoFe/2 nm Cu/0.5 nm Co/2 nm NiFe/1.5 nm Cu/1.5 nm Ru/5 nanometerTa  (9-4)

[0274] In those film structures, the specific resistance of Ru is 30μΩcm while that of Cu is 10 μΩcm. For the electrical shunt effect, Cu of1 nanometer Thick will be equivalent to Ru of 3 nanometer Thick. Inother words, in the films (9-3) and (9-4), the thickness of thehigh-conductivity film is equivalent to 2 nanometers in terms of Cu. Forthe single-layer Cu, its thickness may fall between 0.5 nanometers and 4nanometers. Therefore, for Ru, its thickness may fall between 0.5nanometers and 12 nanometers. However, Ru has a higher specificresistance than Cu and its spin filter effect is much lower than that ofCu. Therefore, for the high-conductivity layer to be adjacent to CoFe,Cu is preferred to Ru. Too thickRu is unfavorable, as notsatisfyingnarrowgaps. For these reasons, therefore, it is desirable thatCu is positioned adjacent to CoFe, while having a thickness of from 0.5to 2 nanometers or so, and the other additional metal layer ispositioned over the Cu layer to give the laminated film for thehigh-conductivity layer.

EXAMPLE 4 Bottom SFSV (with Free CoFe Layer)

5 nanometer Ta/2 nm Ru/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 rim CoFe/2 nmCu/2 nm CoFe/2 nm Cu/5 nanometer Ta  (10-1)

5 nanometer Ta/1 nm Ru/2 nm NiFeCr/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nmCoFe/2 nm Cu/2 nm CoFe/2 nm Cu/5 nanometer Ta  (10-2)

[0275] This is to exemplify other embodiments of the bottom-typestructure of FIG. 6, in which the free layer 122 is of a single-layeredCoFe. The others are the same as in Example 3. The materials of theother layers except the free layer and the thicknesses of those otherlayers are the same as in Example 3. The merits of the single-layeredfree layer of CoFe are the same as in the top-type structure. In thisExample, Ms×t is 3.6 nanometer Tesla in terms of NiFe. When this iscomparedwithMs×t of 4.5 nanometer Tesla, the thickness of the singleCoFe free layer could be 2.5 nanometers and is thin. Even so thin, thesingle CoFe free layer could enjoy good spin filter effect. However, thetwo-layered free layer of NiFe/Co (Fe) shall have a large thickness tobe 4 nm NiFe/0.5 nm Co, and it could not enjoy the spin filter effectfor MR but shall be a simple shunt layer. In addition, NiFe itself alsoexhibits the shunt effect. Therefore, ARs in the two-layered free layeris reduced by 0 to 30%, based on that in the single-layered CoFe freelayer.

[0276] As in the above, since the single-layered CoFe free layer in thisExample could enjoy the MR spin filter effect in a broad range of Ms×t,it is better than the laminated free layer in Example 3.

[0277] In variations of (10-1) and (10-2), the high-conductivity layermay be of a laminate film composed of at least two layers, in place ofthe single-layer high-conductivity layer of Cu as disposed adjacent tothe free layer of CoFe. For example, the laminate film for thehigh-conductivity layer may include Cu/Ru, Cu/Re, Cu/Rh, etc. Theessential object of the two-layered high-conductivity layer is tocontrol the magnetostriction λs in the free layer. This is because, asso mentioned hereinabove, the magnetostriction in the free layer of CoFeis influenced by the distortion of the free layer itself. Reduction inHin is important in the invention. For reducing Hin, the two-layeredhigh-conductivity layer will be effective. Embodiments of the variationsare mentioned below.

5 nanometer Ta/2 nm NiFe/10 nm PtMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/2 nm CoFe/1.5 nm Cu/1.5 nm Ru/5 nanometer Ta  (10-3)

5 nanometer Ta/2 nm NiFe/7 nm IrMn/2 nm CoFe/0.9 nm Ru/2.5 nm CoFe/2 nmCu/2 nm CoFe/1.5 nm Cu/1.5 nm Ru/5 nanometer Ta  (10-4)

[0278] In place of controlling the magnetostriction in CoFe by means ofthe laminated film for the nonmagnetic high-conductivity film as in theabove, the magnetostriction in the free layer could also be controlledby varying the composition of CoFe for the free layer. In general, it iseasy to modify the subbing film for distortion control in the freelayer. However, in bottom-type structures, it is often difficult tofreely select the material for the subbing film for the free layer. Inbottom-type structures, CoFe is laminated on Cu. In those, if Co₉₀Fe₁₀(at. %) is employed, the magnetostriction of the free layer in thenegative side will increase. In order to correct the magnetostriction tothe positive side, Co-rich CoFe is desired. Concretely, desired are CoFefree layers of Co₉₀Fe₁₀ (at. %) to Co₉₆Fe₄ (at. %). However, the Cocontent of the free layer is too large, the Co-rich composition willhave an hcp phase whereby the soft magnetic characteristics of the freelayer will be lowered (that is, Hc in the free layer is increased).Therefore, too Co-rich CoFe alloys such as Co₉₈BFe₂ are unfavorable.

[0279] In those film structures, the specific resistance of Ru is 30μΩcm while that of Cu is 10 μΩcm. For the electrical shunt effect, Cu of1 nanometer Thick will be equivalent to Ru of 3 nanometer Thick. Inother words, in the films (10-3) and (10-4), the thickness of thehigh-conductivity film is equivalent to 2 nanometers in terms of Cu. Forthe single-layer Cu, its thickness may fall between 0.5 nanometers and 4nanometers. Therefore, for Ru, its thickness may fall between 0.5nanometers and 12 nanometers. However, Ru has a higher specificresistance than Cu and its spin filter effect is lower than that of Cu.Therefore, for the high-conductivity layer to be adjacent to CoFe, Cu ispreferred to Ru. Too thick Ru is unfavorable, as not satisfying narrowgaps. For these reasons, therefore, it is desirable that Cu ispositioned adjacent to CoFe, while having a thickness of from 0.5 to 1nanometer or so, and the other additional metal layer is positioned overthe Cu layer to give the laminated film for the high-conductivity layer.

[0280] Second to Sixth Embodiments: Improvement in High-temperatureStability and Reproduction Output Power

[0281] The second to sixth embodiments of the invention are mentionedbelow, which are directed to the improvement in the high-temperaturestability and the reproduction output power.

[0282] First mentioned is the outline of the technical idea common tothe second to sixth embodiments.

[0283]FIG. 17 shows one example of the second to sixth embodiments ofthe invention. In FIG. 17, a lower shield 11 and a lower gap film 12 areprovided on a substrate 10, and a spin valve device 13 is providedthereon. The spin valve device comprises a spin valve film 14 and a pairof longitudinal bias films 15 and a pair of electrodes 16. The spinvalve film 14 comprises nonmagnetic underlayers 141, 142, anantiferromagnetic layer 143, a pinned magnetic layer 144, an interlayer145, a free layer 146 and a protective film 147.

[0284] Table 6 shows the material composition of the antiferromagneticlayer to be coupled with the ferromagnetic layer in SyAF which is thepinned magnetic layer of the invention, the thickness of theantiferromagnetic layer, the magnetic coupling coefficient J at 200° C.,the magnetic coupling bias field H_(UA)* or H_(UA) at 200° C., theblocking temperature Tb, and the resistance change rate ΔR/R in the spinvalve device. Table 7 shows the same data as in Table 6, but in Table 7,the pinned magnetic layer is a conventional, single-layered, pinnedmagnetic layer. Table 8 shows the half-value width of the diffractionpeak from the close-packed plane of the antiferromagnetic layer ascoupled to SyAF in its rocking curve, Δθ; the magnetic couplingcoefficient J at 200° C. to the ferromagnetic layer adjacent to theantiferromagnetic layer in SyAF; and the blocking temperature Tb. TABLE6 Spin Valve Film Constitution: Substrate/5 nanometer Ta/NiFe/CoFe/3 nmCu/2.5 nm CoFe/0.9 nm Ru/2.5 nm CoFe/antiferromagnetic layer/5 nanometerTa Antiferromagnetic Resistance Layer J Blocking Change Thickness(erg/cm²) H_(UA)* (Oe) Temperature Rate ΔR/R Material (nm) at 200° C. at200° C. Tb (° C.) (%) Ir22Mn78 5 0.04 400 250 7.3 (comp. 7 0.045 450 2707.3 case) 1 0.045 450 290 7 20 0.04 400 300 6.5 30 0.035 350 300 5.5Rh20Mn80 7 0.025 250 235 7.1 10 0.035 350 260 6.8 Rh14Ru7M 7 0.02 200225 7.2 n79 10 0.03 300 245 6.8 Pt53Mn47 10 0.02 250 290 7.9 (comp. 150.025 400 320 7.4 case) 20 0.1 >600 350 7 30 0.12 >600 370 6.2 Ni50Mn3015 0.02 250 300 6.8 CrMnPt 15 0.02 200 240 6.9

[0285] Spin valve films with IrMn, RhMn, RhRuMn or CrMnPt: heat-treatedat 270° C. for 1 hour.

[0286] Spin valve films with PtMn or NiMn: heat-treated at 270° C. for10 hours. TABLE 7 Spin Valve Film Constitution: Substrate/5 nanometerTa/NiFe/CoFe/3 nm Cu/2.5 nm CoFe/antiferromagnetic layer/5 nanometer TaAntiferromagnetic Resistance Layer J Blocking Change Thickness (erg/cm²)H_(UA) (Oe) Temperature Rate ΔR/R Material (nm) at 200° C. at 200° C. Tb(° C.) (%) Ir22Mn78 5 0.04 170 250 6.6 10 0.045 190 290 6.2 Pt51Mn49 100.03 130 300 7.2 20 0.1 430 350 6.7 30 0.12 510 370 6.4

[0287] Spin valve films with IrMn: heat-treated at 270° C. for 1 hour.

[0288] Spin valve films with PtMn: heat-treated at 270° C. for 10 hours.TABLE 8 Width of the diffraction peak from the close- Antiferromagneticpacked Layer plane in Blocking Thickness its rocking J (erg/cm²)Temperature Material (nm) curve, Δθ at 200° C. Tb (° C.) Ir22Mn78 5 120.1 210 5 8 0.025 230 5 5 0.045 250 5 3 0.05 250 Rh20Mn80 7 13.5 ˜0 1907 8 0.02 225 7 4 0.025 235

[0289] As in Table 6 and Table 8, we, the present inventors have foundthat (1) when the pinned magnetic layer as coupled to theantiferromagnetic layer has a structure of SyAF and when the compositionof the antiferromagnetic layer is specifically selected, then themagnetic coupling coefficient J at 200° C. could be at least 0.02erg/cm², (2) when the close-packed plane of the antiferromagnetic layeris so oriented that the half-value width of the diffraction peak fromthe close-packed plane of the layer in its rocking curve is reduced,preferably so that it appears at 8 degree or smaller, more preferably at5 degrees or smaller, then the magnetic coupling coefficient J at 200°C. could be increased, (3) when the magnetic thickness of theantiferromagnetic layer is not larger than 20 nanometers, morepreferably not larger than 10 nanometers, then the resistance changerate in the spin valve device having a multi-layered, pinned magneticlayer structure could be increased to be comparable to or higher thanthat in the spin valve device having a single-layered, pinned magneticlayer structure, and (4) when the magnetic coupling coefficient J at200° C. is at least 0.02 erg/cm², then the magnetic coupling biasH_(UA)* at 200° C. could be at least 200 Oe, and, therefore, even thoughthe maximum magnetic field to be applied to the reproduction device,spin valve film, from a recording medium or the like is 200 Oe, thepinned magnetic layer in the spin valve film is still kept stable. Onthe basis of these findings, we have completed the present invention.

[0290]FIG. 18 is a schematic view of the magnetic coupling bias fieldHUA* versus the change in the resistance of the spin valve filmdepending on the applied magnetic field. In FIG. 18, the magneticcoupling bias field HUA* is defined as the maximum magnetic field atwhich the magnetization of the pinned magnetic layer does notsubstantially move, and this is obtained as the intersection of theextended line from the linear region in the low magnetic field side andthe extended line from the linear region in the high magnetic fieldside. The magnetization of the pinned magnetic layer having a magneticcoupling bias field H_(UA)* of at least 200 Oe moves little within themagnetic field range up to 200 Oe in the resistance-magnetic fieldcharacteristics for which an external magnetic field is applied to themagnetization pinned direction, and only the free layer responses to themagnetization to give resistance change.

[0291] In FIG. 18, seen is only the steep resistance change resultingfrom the magnetization response of the free layer in the vicinity of themagnetic field of zero which is the operating point for a magnetic fieldsensor, on the resistance-magnetic field characteristic curve. In this,no resistance change is admitted except the magnetization response ofthe free layer to the applied magnetic field of up to 200 Oe. After thefree layer has been saturated, there occurs no substantial response tothe magnetic field.

[0292] When conventional antiferromagnetic layers of NiO or FeMnCr areused, the constant J could not obtained little at 200° C. On the otherhand, when an antiferromagnetic layer of CrMnPt having a thickness of 30nanometers, the resistance change rate is lower than that inconventional pinned magnetic layers having a single-layered structure,and the layer of CrMnP of that type is unfavorable.

[0293] As in Table 7 showing the data of conventional pinned magneticlayers having a single-layered structure, PtMn gives high H_(UA)* whenits thickness is at least 20 nanometers but its resistance change ratefalls between 6.4 and 6.7% and is relatively low.

[0294] As opposed to those, in the samples of the invention shown inTable 6 in which the antiferromagnetic layer is of any of IrMn, RhMn,RhRuMn, PtMn, NiMn or CrMnPt having a thickness of at most 20nanometers, H_(UA)* at 200° C. is at least 200 Oe, or that is, thesesamples have excellent thermal stability. In addition, the resistancechange rate in those samples is comparable to or higher than that in theconventional samples where the pinned magnetic layer has asingle-layered structure. In the invention, the lowermost limit of thethickness of the antiferromagnetic layer is preferably at least 3nanometers.

[0295]FIG. 19 is a graph of the angle of movement of the magnetizationof the multi-layered, pinned magnetic layer of spin valve films of theinvention with H_(UA)* of 200 oe and that of the single-layered, pinedmagnetic layer of conventional spin valve films with H_(UA) of 500 oe,versus time, in the presence of abias field of 200 Oe at 200° C.perpendicular to the direction of the pinned magnetization. As in FIG.19, it is understood that the time-dependent change at 200° C. in thepinned magnetization in the spin valve films of the invention is smallerthan that in the pinned magnetization in the conventional spin valvefilms where the pinned magnetic layer has a single-layered structure,even though H_(UA)* at 200° C. in the former is 200 Oe and is smallerthan that in the latter of being 510 Oe. This means that the spin valvefilms of the invention are stable.

[0296] The resistance change rate in the spin valve films of theinvention where the antiferromagnetic layer is of an Mn-rich, γ-Mn basedantiferromagnetic material such as IrMn, RhMn or RhRuMn and has athickness of at most 10 nanometers is larger than that in theconventional spin valve films incorporating a single-layered, pinnedmagnetic layer. Those spin valve films of the invention are morepreferred.

[0297] As in Table 6, the spin valve films of the invention with theantiferromagnetic layer having Tb of from 240 to 300° C. have goodthermal stability for the magnetization pinning. Therefore, in thosespin valve films of the invention, since both the ferromagnetic layer Aand the ferromagnetic layer B could be saturated in the same directionby applying thereto a magnetic field larger than the coupling magneticfield of the antiferromagnetically coupling layer at around Tb tothereby freely control the magnetization direction of the pinnedmagnetic layer by the applied magnetic field, the intended magnetizationpinning can be realized even at a temperature not higher than 300° C. atwhich the diffusion between the antiferromagnetically coupling layer andthe ferromagnetic layers A and B could be negligible.

[0298] In order to prevent the diffusion between theantiferromagnetically coupling layer and the ferromagnetic layers A andB and to retard the influences of the diffusion, it is desirable thatthe antiferromagnetically coupling layer has a thickness of larger than0.8 nanometers and contains any of Ru, Rh, Cr, Ir or the like. For thatpurpose, it is effective to use a Co alloy such as CoFe for theferromagnetic layers A and B and to make the level of the surfaceroughness of the antiferromagnetically coupling layer comparable to orlower than the thickness of the layer itself.

[0299] In the thermal treatment for settling the magnetization directionof the pinned magnetic layer, both the magnetic layers A and B must besaturated in the same direction. Therefore, if the ferromagnetic layersA and B are so thinned that their thickness is around 2 nanometers andwhen the thickness of the antiferromagnetically coupling layer is notlarger than 0.8 nanometers, the antiferromagnetically coupling magneticfield of the coupling layer will increase up to about 7 kOe or larger.In that condition, the thermal treatment for settling the magnetizationdirection of the pinned magnetic layer would be difficult in apracticable external magnetic field. For these reasons, it is desirablethat the thickness of the antiferromagnetically coupling layer is largerthan 0.8 nanometers. With such a thick coupling layer, the thermaltreatment for settling the magnetization direction of the pinnedmagnetic layer could be attained in a practicable external magneticfield of, for example, 7 kOe.

[0300] In the samples of the invention in Table 6 all with an SyAF-typeantiferromagnetically coupling layer, the thickness of the ferromagneticlayers A and B of a CoFe alloy is 2.5 nanometers each, and that of theantiferromagnetically coupling layer of Ru is 0.9 nanometers. In those,the antiferromagnetically coupling magnetic field is around 4 kOe, andgood thermal stability could be ensured to the pinned magnetic layer insuch an antiferromagnetic field.

[0301] In the device of the invention, it is desirable that the magneticthickness of the ferromagnetic layer A is nearly the same as or largerthan that of the ferromagnetic layer B. In the device where the magneticthickness of the ferromagnetic layers A and B is nearly the same, themagnetization of the pinned magnetic layer is much more stable againstthe ambient magnetic field and against the longitudinal bias magneticfield than in the device where the magnetic thickness of theferromagnetic layer A is larger than that of the ferromagnetic layer B.

[0302] On the other hand, the device where the magnetic thickness of theferromagnetic layer A is larger than that of the ferromagnetic layer Bcould have better ESD resistance with little pinning magnetizationreversal owing to ESD, than that where the magnetic thickness of theferromagnetic layers A and B is nearly the same. In the former case, itis desirable that the ratio of the magnetic thickness of theferromagnetic layer B to that of the ferromagnetic layer A falls between0.7 and 0.9. For example, when the ferromagnetic layer A is of a CoFealloy of 2.5 nanometers thick, then the ferromagnetic layer A ispreferably of a CoFe alloy of 2 nanometers thick. Even though themagnetic thickness of the ferromagnetic layers A and B is nearly thesame, and even when ESD occurs to cause pinning magnetization reversal,repinnable magnetic disc drives could be realized by incorporatingthereinto a circuit capable of repinning the magnetization of the pinnedmagnetic layer in a predetermined direction in the presence of currentforce (for example, U.S. Pat. No. 5,650,887). For realizing the value Jat 200° C. of at least 0.02 erg/cm², it is desirable to employ anantiferromagnetic layer comprising, as the major phase, a γ-Mn phase ofIrMn, RhMn, RhRuMn or the like or a ordered AuCUII-type phase thatconsists essentially of Mn (of which the Mn content is more preferablyfrom more than 0 but less than 40%); or to employ an antiferromagneticlayer comprising a ordered, face-centered cubic system phase (of CuAuItype) of PtMn, PtPdMn, NiMn or the like (of which the Mn content is morepreferably from 40 to 70%); or to employ a Cr-based antiferromagneticlayer of CrMn, CrAl or the like.

[0303] For ensuring a high value J at 200° C. of at least 0.02 erg/cm²to those alloys in thin antiferromagnetic layers capable of attaining ahigh resistance change rate, the alloys must have a crystal structurewith an oriented close-packed plane.

[0304] From the data in Table 8 that indicate the relationship betweenthe half-value width Δθ of the diffraction peak from the close-packedplane of the antiferromagnetic layer in its rocking curve (this is aparameter of the close-packed plane orientation), Tb and J, it isunderstood that the spin valve films of the invention have a value of Jof at least 0.02 erg/cm² when the half-value width Δθ is not larger than8 degrees. Therefore, it is understood that using those spin valve filmsrealizes the intended magnetoresistance effect heads of the invention.Even for the antiferromagnetic layer of PtMn or the like having aordered, face-centered cubic system phase or for the bcc-typeantiferromagnetic layer of CrMn or the like, the layer could have a highTb and a high J at 200° C. even if it is thin, so far as theclose-packed plane therein is oriented in the same manner as above. Theclose-packed plane as referred to herein is meant to indicate the (111)peak for the fcc phase, the (002) peak for the hcp phase, and the (110)peak for the bcc phase. In the case of PtMn or the like containing aordered, face-centered cubic system phase, the remaining fcc phase shallbe oriented in the (111) plane, or the (111) plane of the ordered,face-centered cubic system phase shall be oriented. The fcc phase andthe hcp phase may have lamination defects.

[0305] As in FIG. 20, the half-value width of the diffraction peak fromthe close-packed plane of the layer in its rocking curve could berepresented by the fluctuation of the close-packed plane spots in thedirection perpendicular to the film surface in the transmission electronmicroscopic images of the cross section of the head, and the half-valuewidth in the rocking curve in X-ray diffractiometry nearly correspondsto the fluctuation angle of the close-packed plane spots in thetransmission electron microscopic images.

[0306] To realize such good close-packed plane orientation, the spinvalve films may be formed in an atmosphere with impurities such asoxygen gas and others therein being minimized as much as possible. Forexample, for forming the films, employable are a deposition method inwhich is used an apparatus capable of pre-degassing the system to alevel of around 10⁻⁹ Torr; a deposition method in which is used asputtering target of which the oxygen content is lowered to at most 500ppm; a substrate bias sputtering method in which a controlled degree ofenergy is applied to the sputtered atoms while the atoms are depositedon the substrate; and a deposition method in which a underlayer of asimple noble metal of, for example, Au, Cu, Ag, Ru, Rh, Ir, Pt, Pd orthe like, or a underlayer of an alloy of any of those noble metals, ofan Ni-based alloy layer of NiFe, NiCu, NiFeCr, NiFeTa or the like isprovided between the alumina cap layer and the spin valve film.

[0307] The above is to explain the outline of the technical field commonto the second to sixth embodiments of the invention as directed to the“improvement in the thermal stability and the reproduction outputpower”.

[0308] The second to sixth embodiments of the invention are described indetail hereunder.

[0309] Second Embodiment:

[0310]FIG. 17 shows one example of the magnetoresistance effect head ofthis Embodiment. As in FIG. 17, a lower shield 11 and a lower gap film12 are formed below an AlTiC (Al₂O₃.TiC) substrate, and a spin valvedevice 13 is formed thereon. The lower shield 11 may be of NiFe, aCo-based amorphous magnetic alloy, an FeAlSi alloy or the like having athickness of from 0.5 to 3 μm, and it is desirable that NiFe or theFeAlSi alloy, if used, is polished to remove surface roughness. Thelower gap layer 12 may be of alumina or aluminium nitride having athickness of from 5 to 100 nanometers.

[0311] The spin valve device comprises a spin valve film 14, a pair oflongitudinal bias films 15 and a pair of electrodes 16. The spin valvefilm comprises a nonmagnetic underlayer 141 of Ta, Nb, Zr, Hf or thelike having a thickness of from 1 to 10 nanometers, an optional secondunderlayer 142 having a thickness of from 0.5 to 5 nanometers, anantiferromagnetic layer 143, a pinned magnetic layer 144, an interlayer145 having a thickness of from 0.5 to 4 nanometers, a free layer 146,and an optional protective film 147 having a thickness of from 0.5 to 10nanometers.

[0312] Above the spin valve device, formed are a gap layer 17 and anupper shield 18. Though not shown, a recording part is formed over them.The gap layer may be of alumina or aluminium nitride having a thicknessof from 5 to 100 nanometers; and the upper shield 18 may be of NiFe, aCo-based amorphous magnetic alloy, an FeAlSi alloy or the like having athickness of from 0.5 to 3 μm.

[0313] Where the antiferromagnetic layer 143 is of a γ-Mn-based, Mn-richalloy of IrMn, RhMn, RhRuMn or the like, or of a ordered, face-centeredcubic system alloy of PtMn, NiMn or the like, it is desirable that theunderlayer 142 is of a metal film of, for example, Cu, Ag, Pt, Au, Rh,Ir, Ni or the like, or an alloy consisting essentially of those metalssuch as AuCu, CuCr or the like; Ni, an Ni-based alloy, NiFe, anNiFe-based alloy or the like such as those described in JP-A 9-229736;or Ru, Ti or the like, or an alloy consisting essentially of thosemetals.

[0314] Where the antiferromagnetic layer 143 is of a Cr-basedantiferromagnetic alloy film, the underlayer 142 may be any of thosementioned above. For the underlayer 142, also suitable is any ofbcc-phase metals of Cr, V, Fe and the like, or of alloys consistingessentially of those metals.

[0315] The pinned magnetic layer 144 is of a three-layered film, whichcomprises two layers of a ferromagnetic layer B, 1441, and aferromagnetic layer A, 1443, as antiferromagnetically coupled to eachother via an antiferromagnetically coupling layer 1442 existingtherebetween. It is desirable to interpose a nonmetallic element such asoxygen, nitrogen or the like between the ferromagnetic layer B and theantiferromagnetic layer 143 or between the ferromagnetic layer B and thelongitudinal bias film of the antiferromagnetic film, as producing largeresistance change. In that case, the thickness of the interlayer intowhich the nonmetallic element is incorporated is preferably from 0.2 to2 nanometers. For example, preferred is a structure of ferromagneticlayer A (or ferromagnetic layer B) /oxide layer/ferromagnetic layer B(or ferromagnetic layer A) in which an oxide interlayer is disposedbetween the ferromagnetic layers A and B.

[0316] The antiferromagnetically coupling layer 1442 may be of a metalof Ru, Rh, Ir or Cr. Preferred are Ru having an extremely largeantiferromagnetically-coupling function; Ru capable of exhibiting itsantiferromagnetically-coupling function in a broad film thickness range;and Cr capable of exhibiting its antiferromagnetically-coupling functionin a broad film thickness range. The thickness of theantiferromagnetically coupling layer is not specifically defined,provided that it is suitable for making the layer exhibit itsantiferromagnetically-coupling function. For this, referred to is thedisclosure in Phy. Rev. Lett., 67, (1991), 3598.

[0317]FIG. 21 is a graph of residual magnetization ratio, Mr/Ms,indicating the reduction in the antiferromagnetic coupling capability ofthe antiferromagnetically coupling layer of Ru after thermal treatment,relative to the thickness of theRulayer. Inthis,theantiferromagneticcouplinglayer of Ru is to couple a ferromagneticlayer of Co and a ferromagnetic layer of a CoFe alloy. Mr/Ms=1 meansthat the coupling layer of Ru has completely lost its antiferromagneticcoupling capability; and Mr/Ms=0 means that the antiferromagneticcoupling of the ferromagnetic layers by the coupling layer of Ru is in acomplete condition.

[0318] As in FIG. 21, it is understood that the thickness of theantiferromagnetic coupling layer of Ru is preferably from more than 0.8nanometers up to 1.2 nanometers. With its thickness falling within thedefined range, the characteristics including theantiferromagnetically-coupling function of the antiferromagneticcoupling layer of Ru are not degraded in any thermal treatment at 250 to300° C. which may be needed for settling the magnetization direction ofthe pinned magnetic layer 144 or may be needed in any other steps offabricating heads and which often induces mutual diffusion between thecoupling layer and the neighboring ferromagnetic layers B and A. If thethickness of the Ru layer is not larger than 0.8 nanometers, someattention must be paid to the mutual diffusion to cause the degradationof the antiferromagnetically-coupling function of the Ru layer. On theother hand, if the thickness is larger than 1.2 nanometers, theantiferromagnetic coupling of the layers B and A by the Ru layer will bedifficult. Where the antiferromagnetically coupling layer is of Cr, itsthickness is also preferably from more than 0.8 nanometers up to 1.2nanometers for the same reasons as those for the Ru layer. Theferromagnetic layers B and A are preferably of Co or a Co-based alloy.

[0319] Where the ferromagnetic layers B and A are of a Co_(1-x)Fe_(x)alloy (0<x≦0.5), a large magnetic coupling coefficient could be ensuredto them with the antiferromagnetic layer 143 of a γ-Mn-based, Mn-richalloy of IrMn, RhMn, RhRuMn or the like, and, in addition, the mutualdiffusion between Ru and theferromagneticlayersBandAcouldbeprevented.Therefore, the alloy is favorable to the layers B and A. If Co is usedfor the layers B and A in place of the CoFe alloy, J will be around ⅔.In addition, as in FIG. 21, the thickness range of theantiferromagnetically coupling layer capable of still maintaining thestable antiferromagnetically-coupling function even after thermaltreatment at 270° C. for 1 hour or so is narrowed for the Co layers, ascompared with that for the CoFe layers.

[0320] The surface smoothness of the antiferromagnetically couplinglayer is also important for the purpose of maintaining the thermalstability for the antiferromagnetically-coupling function of the layer.If the level of the surface roughness of the layer is larger than thethickness of the layer itself even in a minor region of 10 nm² or so,the thermal stability for the antiferromagnetically-coupling function ofthe layer will be lowered. Therefore, it is desirable that the level ofthe surface roughness of the antiferromagnetically coupling layer is notlarger than the thickness of the layer itself.

[0321] Table 9 shows the variation in the sheet resistance Rs of spinvalve films, the sheet resistance change ΔR and the resistance changerate ΔR/R, relative to the varying thicknesses of the ferromagneticlayers A and B. FIG. 22A, FIG. 22B and FIG. 22C are graphs of resistancechange in spin valve films versus the applied magnetic field. TABLE 9Spin Valve Film Constitution: Ta/Au/CuMn/ferromagnetic layer A(CoFe)/0.9 nm Ru/ferromagnetic layer B (CoFe)/2.5 nm Cu/free layer (4 nmCoFe) /Ta Thermal treatment: at 270° C. for 1 hour Thickness ThicknessResistance Sheet of of Change Sheet resistance FerromagneticFerromagnetic Rate resistance Change Layer A Layer B ΔR/R Rs ΔRs (nm)(nm) (%) (Ω) (Ω) 7 7 7.2 7.5 0.54 5 5 8.0 9.8 0.78 3 3 8.6 12 1.03 2 28.4 14.1 1.18 1 1 8.0 15.3 1.22 0.5 0.5 5.9 15.6 0.92

[0322] As in Table 9, the thicknesses of the ferromagnetic layers B andA are preferably from 1 to 5 nanometers for obtaining a high resistancechange rate, but more preferably from 1 to 3 nanometers. With the layersB and A each having a thickness to fall within the preferred range, thepinned magnetic layer is stable to the applied magnetic field (that is,the resistance decreases only a little even in the applied magneticfield of +600 Oe), as in FIGS. 22A to 22C, and, in addition, the sheetresistance Rs of the spin valve films is high and the sheet resistancechange ARs is on a satisfactory level. The reproduction output isproportional to the product of the sense current and the resistancechange, and the resistance change is proportional to the product of theresistance change rate and the sheet resistance of the spin valve film.Therefore, the cases in which only the resistance change rate is largecould not produce high output if their sheet resistance is small. Inother words, in order to attain high output, both the resistance changerate and the sheet resistance must be high.

[0323]FIG. 23A, FIG. 23B and FIG. 23C are graphs of resistance change inspin valve films in which the thickness of the ferromagnetic layer A isfixed to be 3 nanometers and that of the ferromagnetic layer B isvaried, versus the applied magnetic field.

[0324] As in FIGS. 23A to 23C, when the thickness of the ferromagneticlayer A is the same as that of the ferromagnetic layer B, the resistancechange in the spin valve film in a high magnetic field of +600 Oe issmall. In that case, therefore, the pinned magnetic layer is extremelystable to the ambient magnetic field, to the magnetic field from thelongitudinal bias layers and to the applied magnetic field in thermaltreatment for forming the recording part. As so mentioned hereinabove,the problem of magnetization reversal in the pinned magnetic layer to becaused by ESD could be solved by the current circuit as incorporated inthe drive and capable of correcting the pinning magnetization directionto be in a predetermined direction.

[0325] On the other hand, the different thicknesses of the ferromagneticlayers A and B have the following advantages: The first is that thethermal treatment for magnetization pinning is easy, which isindispensable for ensuring the basic constitution of the spin valve filmwhere the magnetization of the free layer is perpendicular to that ofthe pinned magnetic layer. The second is that, when the thickness of theferromagnetic layer B is smaller than that of the ferromagnetic layer A,the resistance change rate is increased, as in Table 10 showing therelationship between the varying thickness of the ferromagnetic layer Band the resistance change rate. The third is that the magnetizationreversal to be caused by ESD occurs little in the pinned magnetic layer,and stable reproduction output is possible even high voltage of aroundthe breakdown voltage. The breakdown voltage as referred to herein ismeant to indicate the voltage at which the spin valve device is brokenand the spin valve device resistance begins to increase. TABLE 10 SpinValve Film Constitution: 5 nanometer Ta/2 nm AuCu/5 nm CoFe/3 nmCu/ferromagnetic layer A (CoFe)/0.9 nm Ru/ferromagnetic layer B(CoFe)/10 nm IrMn/5 nanometer Ta Thickness of Thickness of ResistanceChange 4ferromagnetic Layer ferromagnetic Layer Rate A (rim) B (nm) ΔR/R(%) 3 3 7.3 3 2.5 7.8 3 2 7.7

[0326] For example, when the ferromagnetic layer A, the ferromagneticlayer and the free layer are of any of Co, CoFe and NiFe, while thenonmagnetic spacer layer is of Cu, and when the ratio of the magneticthickness of the layer A to that of the layer B is varied within a rangebetween 0.7 and 0.9 while the thickness of the ferromagnetic layer B is2.5 nanometers, then the spin valve films have good ESD resistance, asin FIGS. 24A and 24B, FIGS. 25A and 25B and Table 11. FIGS. 24A and 24B,and FIGS. 25A and 25B are graphs of resistance versus output in spinvalve devices to which has been applied a simulation ESD voltage by ahuman body model. In FIGS. 24A and 24B, the thickness of theferromagnetic layer A is the same as that of the ferromagnetic layer B;and in FIGS. 25A and 25B, the former is larger than the latter. Table 11shows the ESD data of spin valve devices in test patterns. TABLE 11 SpinValve Film Constitution: 5 nanometer Ta/free layer/3 nm Cu/ferromagneticlayer A/0.9 run Ru/ferromagnetic layer B/10 nm IrMn/5 nanometer TaDevice Constitution: lead-overlaid structure (with no shield) Subbinghard film/longitudinal bias of CoPt/FeCo is formed on the non-patternedlower shield and lower cap, and the electrode spacing is narrower thanthe longitudinal bias spacing. Electrode spacing = 1.3 μm MagneticSpinning Thickness Magneti- Ratio Ferro- Ferro- zation Break- (Ms · t)A/magnetic magnetic Free Reversal down (Ms · t)B Layer A Layer B LayerVoltage Voltage 0.75 2nmCoFe 1.5nmCoFe 3nmCoFe/ not 70 V 1.5nmNiFereversed 0.8 2.5nmCoFe 2nmCoFe 3nmCoFe/ not 75 V 1.5nmNiFe reversed 0.833nmCoFe 2.5nmCoFe 4nmCoFe not 70 V 1.8nmNiFe reversed 0.85 2nmCoFe1.7nmCo 0.5nmCoFe/ not 70 V 4nmNiFe reversed 0.71 2.4nmCoFe 1.7nmCoFe1nmCoFe/ 65 V 75 V 3nmNiFe 0.88 2.4nmCoFe 2.1nmCoFe 1nmCoFe/ 65 V 75 V3nmNiFe 1 3nmCoFe 3nmCoFe 4nmCoFe/ 50 V 75 V 1.8nmNiFe 0.667 3nmCoFe2nmCoFe 3nmCoFe/ 55 V 75 V 1.5nmNiFe 0.93 3nmCoFe 2.8nmCoFe 1nmCoFe/ 55V 70 V 3nmNiFe

[0327] In ESD, a magnetic field essentially of the current magneticfield is applied to the pinned magnetic layer in such manner that themagnetic field intensity to the ferromagnetic layer B is larger thanthat to the ferromagnetic layer A, while, on the other hand, the currentmagnetic field ratio, H(current)_(B)/H(current)_(A) is nearly equal tothe inverse ratio of magnetic thicknesses, (MS·t)_(A)/(MS·t)_(B). Inthat condition, therefore, the magnetic energy changes due to the ESDcurrent field of the ferromagnetic layers A and B cancel, therebyresulting in that the total energy change of:

{(Ms·t)·H(current)}_(A)−{(Ms·t)·H(current)}_(B)

[0328] is reduced. As a result, the magnetization of the pinned magneticlayer could not be moved in the ESD current magnetic field.

[0329] As in FIG. 23C, when the ferromagnetic layer A is 3 nanometersthick and the ferromagnetic layer B is 2 nanometers thick and therefore(Ms·t)_(B)/(Ms·t)_(A)=0.67, then H_(UA)* is lower than that in the caseof FIG. 23A where both the ferromagnetic layers A and B are 3 nanometersthick, and therefore, the thermal stability of the pinned magnetic layerin the case of FIG. 23C is lower than that in the case of FIG. 23A. Inthat case where the magnetic thickness of the ferromagnetic layer B issmaller than that of the ferromagnetic layer A, it is desirable that thecurrent flow direction of the sense current to the pinned magnetic fieldis so selected that the magnetic field from the sense current is in thesame direction as that of the direction of the bias magnetic field fromthe antiferromagnetic field to be applied to the ferromagnetic layer B(or that is, in the same direction as the magnetization direction of theferromagnetic layer B). The reason is because, when the magneticthickness of the ferromagnetic layer A is larger than that of theferromagnetic layer B, a stray magnetic field that corresponds to themagnetic thickness difference between the ferromagnetic field and theferromagnetic field is applied to the free layer, like in conventionalspin valve films having a single-layered pinned magnetic layer, and, asa result, the perpendicular magnetization configuration of the freelayer and the pinned magnetic layer is disturbed by that stray magneticfield. This causes the problem of asymmetry of the reproduction waves,thereby bringing about reproduction output reduction. The stray magneticfield could be canceled by applying a sense current in such a mannerthat the magnetic field by the sense current could be in the samedirection as the direction of the magnetic coupling bias magnetic field,as in FIG. 26 which shows the magnetization and the stray magnetic fieldin spin valve films.

[0330] It is desirable that a simple metal of Cu, Au or Ag or an alloyconsisting essentially of those metals is used for the nonmagneticspacer layer. Basically, the thickness of the nonmagnetic spacer layermay well be in a range between 1 and 10 nanometers or so, capable ofensuring the necessary resistance change rate. Especially in the spinvalve films of the invention, it is desirable that the thickness of thenonmagnetic spacer layer falls between 1.5 nanometers and 2.5nanometers, as being able to control the interlayer-coupling magneticfield that may be generated between the pinned magnetic layer and thefree magnetic layer, to the level of at most 15 oe, and as being able toproduce a high resistance change rate.

[0331] For the free layer, employable is any of Co, a Co alloy such asCoFe, CoNi, CoFeNi or the like, or a laminate film of those metals andalloys. For example, employable is a laminate film composed of an NiFealloy layer and a thin Co layer, in which the thin Co layer is to beadjacent to the nonmagnetic interlayer. It is desirable that thethickness of the free layer falls between 1 and 10 nanometers.

[0332] Table 12 shows a varying thickness of the free layer versus theresistance change rate AR/R, in which the thickness of the pinnedmagnetic layer is fixed to be 2.5 nanometers. As in Table 12, it isunderstood that, in the invention, the thickness of the free layer ismore preferably from 2 to 5 nanometers, as giving high resistance changerates. TABLE 12 Change Rate Resistance ΔR/R** (%) Thickness Thickness ofChange Rate (laminated of Ferromagnetic ΔR/R* free layer Free Layer A =(%) (single- with 1 nm Co Layer Ferromagnetic layered free adjacent to(nm) Layer B (nm) layer of CoFe) interlayer) 1 2.5 6.2 5.7 2 2.5 7.5 7.03 2.5 7.9 7.2 4 2.5 7.8 7.2 5 2.5 7.5 7.1 6 2.5 6.9 6.4 7 2.5 6.6 6.0

[0333] Table 13 shows a varying thickness of the ferromagnetic layer Aof the pinned magnetic layer versus the resistance change rate ΔR/R, inwhich the thickness of the free layer is fixed to be 4 nanometers. As inTable 13, it is desirable that the thickness, t(F), of the free layer offrom 2 to 5 nanometer Thick and the thickness, t(P) of the ferromagneticlayer A satisfy the following condition:

−0.33≦{t(F)−t(P)}/t(F)≦0.67,

[0334] for producing a high resistance change rate. TABLE 13 Thicknessof Thickness of Ferromagnetic Resistance Free Layer, Layer A, t(P)Change Rate, (t(F)- t(F) (nm) (nm) ΔR/R(%) t(P))/t(F) 4.5 1 4.7 0.78 4.51.5 6.9 0.67 4.5 2 7.1 0.56 4.5 3 7.9 0.33 4.5 4 7.7 0.11 4.5 5 7.3−0.11 4.5 6 6.8 −0.33 4.5 7 5.9 −0.66

[0335] For the protective film, used is any of metals of Ta, Nb, Zr, Cr,Hf, Ti, Mo, W and the like, or their alloys, or their oxides, nitrides,etc. Preferred are high-resistance protective films of metal oxides ornitrides, for example, NiFe oxides, aluminium oxides, tantalum oxidesand others, as giving high resistance change rates. Regarding itsthickness, it is desirable that the protective film is as thin aspossible and has a thickness of from 0.3 to 4 nanometers. This isbecause, as will be mentioned hereunder, such a thin protective film iseasy to remove through etching for forming electrodes and longitudinalbias layers. As the protective layer, also usable are single-layered orlaminated films of simple noble metals such as Ag, Au, Ru, Ir, Cu, Pt,Pd, Re and others, or of their alloys. For example, for the free layerof CoFe, usable are protective layers of Cu/Ru, Cu, Au, Cu alloys, etc.;for the free layer of NiFe, usable are protective layers of Ag, Ru,Ru/Ag, Ru/Cu, Cu, etc. Over the protective film of oxides, nitrides ornoble metals, an additional, high-resistance protective film of Ta orthe like may be optionally formed.

[0336] For making the magnetization direction of the pinned magneticlayer perpendicular to that of the free layer, for example, employableis the following method. Where the antiferromagnetic layer 143 is of aγ-Mn-based, Mn-rich alloy such as IrMn, RhMn, RhRuMn or the like, thedeposition of the constituent layers of the spin valve film to theantiferromagnetically coupling layer 1442 is carried out in a magneticfield as applied in the direction of the width of the spin valve deviceto be produced, or that is, in the height direction, and thereafter theresulting layered structure is subjected to thermal treatment forunifying the coupling bias magnetic field due to the antiferromagneticlayer 143 in the height direction. The thermal treatment for unifyingthe coupling bias magnetic field in the height direction may be carriedout immediately after the formation of the antiferromagnetic layer B.However, since the antiferromagnetically coupling layer of Ru or thelike is more resistant to oxidation, it is more desirable that thethermal treatment is effected after the formation of the coupling layer1442. Preferably, the thermal treatment is effected still in vacuum, orthat is, without leaking the vacuum for the previous deposition, at atemperature higher than Tb and for a short period of time, morepreferably within at most 10 minutes, in a magnetic field in which theferromagnetic layer B could be completely saturated. For example, forIrMn having Tb of 300° C., the thermal treatment may be effected at 350°C. for 1 minute or so.

[0337] Next, still in vacuum, a magnetic field is applied in thedirection of the track width of the spin valve device being formed, atleast during the formation of the free layer, and thereafter, theremaining films of the spin valve device are formed. The same shallapply to the case where the antiferromagnetic layer is of a orderedalloy of PtMn or NiMn. For this case, however, the process will somewhatdiffer from that for the case of the γ-Mn-based antiferromagnetic layernoted above. In this case, the deposition step up to the formation ofthe antiferromagnetic layer B does not always require a magnetic field,but the thermal treatment after the step must be effected at hightemperatures of at least 200° C., preferably falling between 270 and350° C., for a few hours, preferably for 1 to 20 hours. After thethermal treatment, a magnetic field is applied during the step offorming the free layer and thereafter the remaining layers of the spinvalve film are formed, in the same manner as in the previous case.

[0338] In any case, the thermal treatment for the antiferromagneticlayer may be effected after the formation of the spin valve film. Whenthe thermal treatment is effected after the film formation, it isdesirable that a magnetic field higher than the coupling magnetic fieldof the antiferromagnetically coupling layer 1442 is applied to the spinvalve film being subjected to the thermal treatment so that themagnetizations of both the ferromagnetic layer A and the ferromagneticlayer B are saturated completely in the same direction (that is, in theheight direction). For example, where the antiferromagnetic layerB/antiferromagnetic layer B is in the form of 2 nm CoFe/0.9 nm Ru/2 nmCoFe, the coupling magnetic field of Ru is about 6 kOe. Therefore, inthis case, the magnetic field to be applied during the thermal treatmentis preferably at least 7 kOe. In order to reduce the magnetic field forthe thermal treatment, it is desirable to finish the thermal treatmentbefore the spin valve film is worked into the form of a device. Thethermal treatment of the device as worked from the film requires astronger magnetic field for saturating the ferromagnetic layers A and Bbecause of the reversal magnetic field intrinsic to the shape of thedevice.

[0339] In the method noted above, the magnetization of the pinnedmagnetic layer 144 is pinned in a predetermined direction. However, theheat treatment in the method is too strong, the easy axis of the freelayer 146 and even that of the lower shield 11 will also be pinned inthe height direction of the spin valve device, like in the pinnedmagnetic layer. If so, it will be difficult to make the magnetizationdirection of the free layer perpendicular to that of the pinned magneticlayer. In order to fix the easy axis of the free layer and that of thelower shield in the direction of the track width, it is desirable toapply to the free layer and the shield, the minimum magnetic fieldnecessary for saturating the shield and the free layer in the directionof the track width, for example, a magnetic field of from 100 to 300 oeor so, in the resist curing step for fabricating recording heads,thereby stabilizing the easy axis of the shield and that of the freelayer in the direction of the track width. Also preferably, the lowershield is previously subjected to thermal treatment before thecompletion of the spin valve film, thereby stabilizing its easy axis inthe direction of the track width.

[0340] In the abutted junction type device of FIG. 17, in which thetrack edges of the free layer are removed and longitudinal bias layersare provided in place of the removed edges, the longitudinal bias layersmay be of a hard magnetic film of, for example, CoPt, CoPtCr or the likeas formed on a underlayer of, for example, Cr, FeCo or the like, or maybe of a laminated, hard ferromagnetic film composed of a ferromagneticlayer 151 and an antiferromagnetic layer 152 as laminated in that order.Alternatively, the antiferromagnetic layer 152 may be formed first, andthereafter the ferromagnetic layer 151 may be laminated thereover. Inorder to obtain a steep reproduction sensitivity profile capable ofmeeting the coming narrow tracks in the art, at the track edges, it isdesirable that the magnetic thickness ratio of the ferromagnetic,longitudinal bias layer, or that is, the hard magnetic layer or theferromagnetic bias layer as magnetically coupled by an antiferromagneticlayer, to the free layer, (MSt)LB/(MSt)F, is defined to be at most 2.Where the free layer is thinned to have a thickness of from 2 to 5nanometers and have a magnetic thickness of from 3 to 6 nanometer Tesla,the ferromagnetic, longitudinal bias layers shall also be thinned inorder that the ratio (Ms·t)_(LB)/(MS·t)_(F) is made to be at most 2. Forexample, the ferromagnetic, longitudinal bias layer shall have amagnetic thickness of at most 12 nanometer Tesla.

[0341] In general, however, when the hard magnetic film is thinned tohave a thickness of 10 nanometers or so, then it could hardly maintainhigh coercive force. For example, for a hard magnetic film of CoPthaving Ms of 1 T, it has a high coercive force of 2000 oe when itsthickness is 20 nanometers, but its coercive force decreases to 800 Oewhen its thickness is 10 nanometers. On the other hand, in thelongitudinal bias layer of a type of ferromagneticlayer/antiferromagnetic layer, the magnetic coupling bias fieldincreases with the reduction in the thickness of the ferromagnetic layer151, whereby the two layers are coupled more firmly. For example, forthe longitudinal bias layer having a laminated structure of NiFe with Msof 1 T and IrMn of 7 nanometers thick, its coercive force is 80 oe whenits thickness is 20 nanometers, but increases up to 160 Oe when itsthickness is 10 nanometers. The value of 160 oe is an effective value inconventional MR heads. Therefore, in the region where the free layer isthin, for example, having a thickness of at most 5 nanometers, it isdesirable to employ the longitudinal bias layer of the type offerromagnetic layer/antiferromagnetic layer.

[0342] In addition, in the longitudinal bias layer of the type offerromagnetic layer 151/antiferromagnetic layer 152, it is furtherdesirable that the saturation magnetization of the ferromagnetic layer151 is nearly comparable to or larger than that of the free layer inorder to completely remove the Barkhausen noise in a smallest possiblelongitudinal bias field. The ferromagnetic film 151 may be of an NiFealloy, but is more preferably of an NiFeCo alloy, a CoFe alloy, Co orthe like having a larger saturation magnetization. If a film having asmall saturation magnetization is used for the ferromagnetic film 151and if the Barkhausen noise is removed by increasing its thickness toenlarge the stray magnetic field, the reproduction output will lowerespecially in narrow track width.

[0343] In FIG. 17, the longitudinal bias layers are formed withoutcompletely removing the entire spin valve film. Apart from theillustrated case, even the underlayer 141 may be removed throughetching. However, in order to maintain good crystallinity of theferromagnetic layer, it is desirable that the etching depth before theformation of the longitudinal bias layers is at most above theunderlayer 142 so as to take advantage of the crystallinity-improvingeffect of the layer 142. From the viewpoint of film thickness control,it is desirable that the thicker antiferromagnetic layer 143 is etchedin some degree and thereafter the magnetic coupling bias is attenuatedso as to obtain, longitudinal bias layers having good hard magneticproperties. As the case may be, after the nonmagnetic spacer layer ispartly etched, and a longitudinal bias layers of ferromagnetic film151/antiferromagnetic film 152 may be formed thereover. For the purposeof improving the crystallinity or for the purpose of attenuating themagnetic coupling between the pinned magnetic layer or theantiferromagnetic layer 143 and the longitudinal bias layer, anextremely thin underlayer 153, like the underlayer 143, may be providedbelow the ferromagnetic film 151. For the purpose of minimizing thereduction in the magnetic coupling between the free layer and thelongitudinal bias layer, the thickness of the underlayer 153 ispreferably at most 10 nanometers.

[0344] Where the hard magnetic film is employed, it is also desirablethat the saturation magnetization of the free layer is comparable tothat of the hard magnetic layer. In general, however, it is difficult toprepare a hard magnetic film having high saturation magnetization thatis comparable to the free layer of CoFe or the like generally havinghigh saturation magnetization. For this, effective is a method of usinga subbing film of FeCo or the like having high saturation magnetizationfor the hard magnetic film to thereby keep the good balance ofsaturation magnetization between the subbed hard magnetic film and thefree layer, for the purpose of removing the Barkhausen noise in a smalllongitudinal bias magnetic field.

[0345] For the antiferromagnetic film 152, employable is the sameantiferromagnetic substance as that for the spin valve film. However,the magnetic coupling bias field for the antiferromagnetic layer in thespin valve film is in the height direction while that for theantiferromagnetic film 152 in the longitudinal bias layer is in thetrack width direction, or that is, the two must be perpendicular to eachother. Therefore, for example, the two are made to have a differentblocking temperature Tb, and the magnetic coupling bias direction of theantiferromagnetic layer having a higher Tb is first settled throughthermal treatment, and thereafter the antiferromagnetic film having alower Tb is subjected to thermal treatment at lower temperatures. Inthat condition, while the magnetic coupling bias direction of theantiferromagnetic layer having a higher Tb is kept stable as it is, themagnetic coupling bias direction of the antiferromagnetic film having alower Tb is settled, whereby the magnetic coupling bias fields of thetwo could be made perpendicular to each other.

[0346] Concretely, the antiferromagnetic film 152 may be anantiferromagnetic film of PtMn, PdPtMn or the like capable of expressingHUA through thermal treatment. For this, however, more preferred is anyof RhMn, IrMn, RhRuMn, FeMn or the like having Tb of from 200 to 300° C,since they can be subjected to thermal treatment at temperatures atwhich the pinned magnetic layer is stable. For the antiferromagneticlayer in the spin valve film, preferred are antiferromagnetic substanceshaving a higher Tb, such as IrMn, PtMn, PtPdMn, etc. Using thosepreferred antiferromagnetic substances, the magnetic coupling biasdirection of the antiferromagnetic film 152 could be well settled in thetrack width direction without disturbing the magnetization direction ofthe pinned magnetic layer in the spin valve film in the step of thermaltreatment for resist curing noted above. Specifically, because of thecharacteristic of the invention where the pinning magnetization israpidly stabilized at temperatures not higher than the blockingtemperature, the longitudinal bias and the magnetization of the pinnedmagnetic layer could be made well perpendicular to each other eventhough the difference in the blocking temperature between the bothantiferromagnetic films is only tens ° C. When IrMn, FeMn, RhMn, RhRuMn,CrMnPt, CrMn or the like capable of producing a magnetic coupling biasfield during deposition them in a magnetic field is used for theantiferromagnetic film 152, it does not require any additional thermaltreatment. Therefore, the antiferromagnetic film 152 of any of thosesubstances, not requiring additional heat treatment, does not disturbthe bias magnetic field direction of the antiferromagnetic layer 143 inthe spin valve film. To be combined with the film 152 of that type, anyand every type of antiferromagnetic substances could be used for theantiferromagnetic layer 143 in the spin valve film, and in anycombination of the two, the longitudinal bias direction and themagnetization direction of the pinned magnetic layer could be made wellperpendicular to each other.

[0347] On the other hand, as in FIG. 27, only the protective film 147 atthe track edges of the free layer may be etched away, and anantiferromagnetic film may be laminated thereover through magneticcoupling to apply a longitudinal bias to the free layer. In this case,it is desirable that the longitudinal bias layer 15 comprises anantiferromagnetic layer 152 and a buffer layer 1511, which is aunderlayer for enhancing the magnetic coupling with the free layer. Thebuffer layer 1511 is preferably a ferromagnetic layer of Fe, Co, Ni orthe like. For settling the magnetization direction of the longitudinalbias in this case, the same as in the above-mentioned case offerromagnetic layer 151/antiferromagnetic layer 152 could apply also tothis case. The longitudinal biasing system using such a ferromagneticlayer is advantageous in that the Barkhausen noise is effectivelyremoved therein, without generating any unnecessary longitudinal biasmagnetic field to lower the sensitivity of heads as in the system usinga hard magnetic film.

[0348] Third Embodiment:

[0349]FIG. 28 shows the third embodiment of the invention. In FIG. 28,the structure of the spin valve film differs from that in FIG. 21. InFIG. 27, a spin valve film 14 formed on a lower gap 12, and comprises anonmagnetic underlayer 141 of Ta, Nb, Zr, Hf or the like having athickness of from 1 to 10 nanometers, an optional second underlayer 142having a thickness of from 0.5 to 5 nanometers, a free layer 146, aninterlayer 145 having a thickness of from 0.5 to 4 nanometers, a pinnedmagnetic layer 144, an antiferromagnetic layer 143, and an optionalprotective film 147 having a thickness of from 0.5 to 10 nanometers. Inthis, free layer 146, the interlayer 145, the pinned magnetic layer 144and the antiferromagnetic layer 143 are the same as those in the secondembodiment.

[0350] Where the underlayer 142 is of Au, Cu, Ru, Cr, Ni, Ag, Pt or Rh,or an alloy consisting essentially of those metals, the thermalstability for the resistance change rate could be increased especiallywhen the free layer is of a CoFe alloy.

[0351] In FIG. 27, a pair of longitudinal bias layers 15 and a pair ofelectrodes 16 which are the same as those in FIG. 21 constitute, alongwith the spin valve film 14, a spin valve device 13 Like in FIG. 21, anupper gap layer 17 and an upper shield 18 are formed to cover the device13.

[0352] Fourth Embodiment:

[0353]FIG. 29 shows still another embodiment of the invention, which isapplied to a dual-type spin valve structure.

[0354] In FIG. 29, a pair of longitudinal bias layers 15, a pair ofelectrodes 16, a longitudinal bias layer 15, and a spin valve device 13comprising a spin valve film 14 are formed on a lower shield 11 and alower gap 12, and an upper gap 17 and an upper shield 18 are formed overthem, like in FIG. 21 for the second embodiment and in FIG. 27 for thethird embodiment. However, the structure of FIG. 29 differs from thoseof FIG. 21 and FIG. 27 in point of the spacing between the electrodes 16and of the constitution of the spin valve film 14.

[0355] The spin valve film 14 comprises a nonmagnetic underlayer 141 ofTa, Nb, Zr, Hf or the like having a thickness of from 1 to 10nanometers, an optional second underlayer 142 having a thickness of from0.5 to 5 nanometers, an antiferromagnetic layer 143, a pinned magneticlayer 144, an interlayer 145 having a thickness of from 0.5 to 4nanometers, a free layer 146, a second interlayer 148 having a thicknessof from 0.5 to 4 nanometers, a second pinned magnetic layer 149, asecond antiferromagnetic layer 150, and an optional protective layer 147having a thickness of from 0.5 to 10 nanometers.

[0356] At least one of the pinned magnetic layer 144 and the pinnedmagnetic layer 149 is a laminated, pinned magnetic layer, whichcomprises a ferromagnetic layer A, an antiferromagnetically couplinglayer and a ferromagnetic layer B as in FIG. 17. In this, employable isany of 1) a combination of an SyAF-type pinned magnetic layer for thepinned magnetic layer 149 and a conventional, single-layered pinnedmagnetic layer for the pinned magnetic layer 144, 2) contrary to 1), acombination of an SyAF-type pinned magnetic layer for the pinnedmagnetic layer 144 and a conventional, single-layered pinned magneticlayer for the pinned magnetic layer 149, or 3) a combination ofSyAF-type pinned magnetic layers for both the pinned magnetic layer 149and the pinned magnetic layer 144.

[0357] The longitudinal bias layers 15 have a so-called abutted junctiontype device structure. These may be formed according to a lift-offmethod, like in FIG. 17, FIG. 27 and FIG. 28. Briefly, the track edgesof the spin valve film are etched away via a photo-resist mask, andthereafter the longitudinal bias layers 15 are formed throughsputtering, vapor deposition, ion beaming or the like. In this process,the etching removal of the spin valve film 14 is preferably so effectedthat at least the conductor layer part of the spin valve film 14 is leftas it is without being removed. For example, when the antiferromagneticlayer 143 is of a γ-Mn-based alloy such as IrMn, it is desirable that atleast a part of the antiferromagnetic layer 143 is left as it is.

[0358] If the conductor part is left in the track edges, the contactresistance of the abutted junction structure is lowered, and thereforethe resistance of the spin valve device 13 could be lowered with ease.With the low-resistance spin valve device 13, heads could have highresistance to static electricity. Needless-to-say, the spin valve filmat the track edges may be completely etched away with no problem to formthe longitudinal bias layers.

[0359] The electrodes 16 may be formed along with the longitudinal biaslayers in one and the same lift-off method. In this case, the spacingbetween the electrodes is nearly the same as that between thelongitudinal bias layers. Alternatively, the formation of the electrodesmay be effected separately from that of the longitudinal bias layers toform a so-called lead-overlaid structure in which the spacing betweenthe electrodes is narrower than that between the longitudinal biaslayers. The merit of the lead-overlaid structure is that, especiallywhen the longitudinal bias layers are hard magnetic layers, theinfluence of the stray magnetic field from the hard magnetic layer couldbe trapped in the vicinity around the track edges in which theelectrodes and the spin valve film are laminated, whereby thesensitivity profile of the reproduction track width (this is defined bythe electrode spacing) in the track width direction could be sharper andits accuracy could be augmented. In particular, for high-densityrecording for which the reproduction track width shall be of asub-micron level, the merit of the structure is more remarkable than inthe prior art technique. Naturally, the lead-overlaid structure couldapply to the embodiments of FIG. 21 and FIG. 27.

[0360] Fifth Embodiment:

[0361]FIG. 30 shows still another embodiment of the invention. Like inthe second embodiment shown in FIG. 21, a lower shield anda lower cap(not shown) are formed ona substrate (not shown), a spin valve film 13is formed thereover, and an upper cap, an upper shield and a recordingpart (all not shown) are formed still thereover. At the both track edgesof the spin valve film 13, formed are a pair of longitudinal bias layers15 and a pair of electrodes 16. One example of the longitudinal biaslayers is illustrated, which is a laminate film comprising a underlayer153, a ferromagnetic film 151 and an antiferromagnetic film 152.Naturally, the longitudinal bias layers may be of a hard magnetic filmof CoPt or the like.

[0362] The electrodes 16 are formed of a material at least containing alow-resistance metal, such as Ta/Au/Ta or the like. In the illustratedcase, the electrode spacing LD is narrower than the longitudinal biaslayer spacing HMD, and the spin valve film 13 and the electrodes 16 havea region in which they are face-to-face contacted, in the vicinity ofthe both track edges. The longitudinal bias layers and the electrodesare generally formed in a lift-off method, but theymaybe also formedthrough ion milling, reactive ion etching or the like. Thoughcomplicated, a dry process is suitable for forming precision electrodes.

[0363] In the region of the spin valve film 13 just below the electrodes16 where the longitudinal bias layers 15 do not exist, when theresistance of the electrodes is much smaller than that of the spin valvefilm, for example, when the former is at most 1/10 of the latter, thenthe reproduction sensitivity is greatly lowered in the region except theelectrode spacing region, for example, in the region of the spin valvefilm just below the electrodes, if the magnetization of the free layer146 in the spin valve film is settled nearly in the track widthdirection when the ambient magnetic field is zero. In that condition,therefore, the reproduction track width could be defined by theelectrode spacing LD, whereby a steep reproduction sensitivity profilecould be realized at the track edges.

[0364] In addition, in the illustrated constitution, since theface-to-face contact region for the spin valve film 13 and theelectrodes 16 could be much larger than in an ordinary abutted junctiontype constitution, the contact resistance between the electrodes and thespin valve film could be well minimized. With this, therefore,low-resistance spin valve devices could be realized, and even low-noise,ESD-resistant magnetoresistance effect heads could be realized.

[0365] For further narrowing the reproduction track width for thepurpose of increasing the recording density in coming devices, theelectrode spacing LD must be narrowed. On the other hand, however, ifthe electrode spacing is too narrow, it will be difficult to much morereduce the width or the height of the device. Therefore, it is desirablethat HD is larger than LD for increasing the yield of heads. Concretely,regarding the height which will be a dimension-determinant factor inmachine working for the purpose of increasing the yield of heads in massproduction, the height must be at least around 0.5 μm or larger. Whenthe reproduction track width is narrowed to 0.5 μm or smaller, it isdesirable that HD is settled larger than LD. However, this will bringabout the following problems.

[0366] The first is that, since the resistance of the spin valve filmregion for reproduction is reduced, the reproduction output is reduced.This problem could be overcome by increasing the sheet resistance of thespin valve film. In an ordinary SyAF-type pinned layer, the thickness ofthe pinned layer is larger than a conventional, single-layered pinnedmagnetic layer. Therefore, increasing the sheet resistance of the spinvalve film having such an ordinary SyAF-type pinned layer is difficult.However, as in Table 14 and Table 15, since the sum total of thethicknesses of the pinned magnetic layer, the nonmagnetic spacer layerand the free layer is limited to at most 14 nanometers in the invention,both high sheet resistance of at least 16 Ω and high resistance changerate of at least 8% could be attained. TABLE 14 Spin Valve FilmConstitution: 5 nanometer Ta/2 nm Au/7 nm IrMn/ferromagnetic layerB/antiferromagnetically coupling layer/ferromagnetic layer A/nonmagneticspacer layer/free layer/Ta Thickness Thickness Thickness of Non- TotalThickness of Ferro- Thickness of Ferro- magnetic Thickness ofFerromagnetic magnetic of Coupling magnetic spacer of Free Layer B toLayer B (nm) Layer (nm) Layer A (nm) layer (nm) Layer (nm) Free Layer(nm) 2 nm CoFe 0.9 nm Ru 2 nm CoFe 2 nm Cu 0.5 nm CoFe/ 9.9 2.5 nm NiFe1.5 nm CoFe 0.8 nm Ru 2 nm CoFe 2 nm Cu 0.5 nm CoFe/ 10.8 4 nm NiFe 1.5nm CoFe 0.9 nm Ru 2 nm CoFe 2.5 nm Cu 3 nm CoFe 9.9 2 nm CoFe 0.9 nm Ru2 nm CoFe 2 nm Cu 1 nm Co/ 12.9 5 nm NiFe 1.5 nm CoFe 0.9 nm Ru 1.5 nmCoFe 2 nm Cu 1 nm Co/ 9.9 3 nm NiFe 2 nm CoFe 0.9 nm Ru 2.5 nm CoFe 2 nmCu 3 nm CoFe 10.4 2 nm CoFe 1 nm Ru 2.5 nm CoFe 2.5 nm Cu 1 nm Co/ 13 4nm NiFe 2.2 nm CoFe 0.8 nm Ru 2.5 nm CoFe 2 nm Cu 2 nm CoFe/ 14 4.5 nmNiFe 3 nm CoFe 0.9 nm Ru 3 nm CoFe 3 nm Cu 1 nm CoFe/ 17.8 7 nm NiFe 3nm CoFe 0.9 nm Ru 3 nm CoFe 3 nm Cu 3 nm CoFe/ 14.8 2 nm NiFe 2.5 nmCoFe 0.8 nm Ru 3 nm CoFe 2.5 nm Cu 1 nm CoFe/ 16.8 7 nm NiFe 3 nm CoFe0.7 nm Ru 3 nm CoFe 3 nm Cu 5 nm CoFe 14.7

[0367] TABLE 15 Spin Valve Film Constitution: 5 nanometer Ta/2 nmNiFe/7.5 nm PtMn/ferromagnetic layer B/antiferromagnetically couplinglayer/ferro- magnetic layer A/nonmagnetic spacer layer/free layer/TaThickness Thickness Thickness of Non- Total Thickness of Ferro-Thickness of Ferro- magnetic Thickness of Ferromagnetic magnetic ofCoupling magnetic spacer of Free Layer B to Layer B (nm) Layer (nm)Layer A (nm) layer (nm) Layer (nm) Free Layer (nm) 2 nm Co 0.9 nm Ru 2nm Co 2.5 nm Cu 1 nm Co/2 nm 10.4 NiFe 2 nm Co 0.9 nm Ru 2 nm Co 2.5 nmCu 0.5 nm Co/ 9.9 2 nm NiFe 2 nm CoFe 0.9 nm Ru 2 nm CoFe 2.5 nm Cu 1 nmCoFe/ 9.7 2 nm NiFe 2 nm CoFe 0.9 nm Ru 2 nm CoFe 2.5 nm Cu 3 nm CoFe10.4

[0368] In order to realize high resistance change rates in suchultra-thin spin valve films, it is desirable that 1) the ferromagneticlayers A and B in the pinned magnetic layer are of an alloy of CoFe,CoNi or CoFeNi having a stable fcc phase, 2) even in the free layer,used is Co or an alloy of CoFe, CoNi or CoFeNi at least in the vicinityof the interface between the free layer and the nonmagnetic spacerlayer, and 3) in the antiferromagnetic film, used is anantiferromagnetic layer containing a noble metal element, such as PtMn,PtPdMn, IrMn, RhMn, RhRuMn or the like.

[0369] The second problem with HD larger than LD is the Barkhausennoise. In a conventional abutted junction type spin valve device inwhich the electrode spacing is nearly the same as the longitudinal biasfilm spacing HMD, HMD is smaller than HD whereby the free layer isrectangular, having a longer side in the HD direction, and themagnetization direction of the free layer is readily oriented in theheight direction in which the intensity of the antimagnetic field issmaller. As a result, a Barkhausen noise occurs in this. As opposed tothis, since side of the rectangular spin valve film in the invention islonger in the track width direction as HMD is larger than HD therein,the magnetization direction of the free layer is prevented from beingoriented in the height direction. As a result, removing the Barkhausennoise from the device of the invention is easy. For these reasons, theyield of heads comprising the device of the invention is high.

[0370] Concretely, cases of 1) HD=0.5 μm, LD=0.45 μm, HMD=1.3 μm, and 2)HD=0.4 μm, LD=0.35 μm, HMD=0.8 μm much enjoy the effect of theinvention.

[0371] In the constitution of FIG. 29, the pinned magnetic layer isdisposed between the free layer and the substrate. The same mentionedherein shall apply to other cases where the free layer is disposedbetween the substrate and the pinned magnetic layer.

[0372] Sixth Embodiment:

[0373]FIG. 31 shows still another embodiment of the invention. Asubstrate, a lower shield and a lower gap (all not shown) are formed,and a pair of longitudinal bias layers 15 are formed thereon accordingto a lift-off method or to any other dry process of ion milling,reactive ion etching or the like. In FIG. 29, one example of thelongitudinal bias layers is shown, which is a laminate comprising aunderlayer 153 suitable to an antiferromagnetic layer, anantiferromagnetic film 152 of IrMn, RhMn, CrMn or the like, and aferromagnetic film 151 of CoFe, NiFe, Co or the like, as in the secondembodiment. To this case, any other types of longitudinal bias layerssuch as those illustrated in the second embodiment could apply.

[0374] A spin valve film 13 is formed over the structure formed in thatmanner. In the spin valve film 13, it is desirable that the free layer143 is disposed nearer to the substrate than the pinned magnetic layerso as to facilitate the easy contact between the longitudinal biaslayers 15 and the free layer 143. This is for the purpose of moreeffectively applying the bias magnetic field from the longitudinal biaslayers to the free layer 143. It is also desirable that the thickness ofthe underlayers 141 and 142 below the free layer 143 is 10 nanometers.This is also for the purpose of more effectively applying the biasmagnetic field from the longitudinal bias layers to the free layer 143.It is further desirable that the face-to-face contact region between thespin valve film 13 and the longitudinal bias layers 15 is minimized asmuch as possible to prevent the Barkhausen noise.

[0375] Above the spin valve film 13, formed are a pair of electrodes 16according to a lift-off method, an ion milling method or a reactive ionetching method. Though not shown, an upper gap, an upper shield and arecording part are formed over the film 13.

[0376] Like in the fifth embodiment, HD is larger than LD but is smallerthan HMD. With that constitution, reproducing heads suitable to narrowtrack width could be fabricated at high yields. Since the totalthickness of the pinned magnetic layer, the nonmagnetic spacer layer andthe free layer is at most 14 nanometers, the resistance of the spinvalve film 13 is increased and the reproduction output is increased.With that constitution, high-sensitivity magnetoresistance effect headscan be obtained.

[0377] Seventh Embodiment: Improvement in Thermal Stability and MirrorReflectivity, and Reduction in Magnetostriction

[0378] From the viewpoint of improving the thermal stability and themirror reflectivity and of reducing the magnetostriction, the seventhembodiment of the invention is described below.

[0379] Prior to introducing this embodiment, the problems which we, theinventors have recognized in the process of achieving this embodimentare mentioned.

[0380] For practical use of high-performance spin valve films(hereinafter referred to as SV films), we, the inventors have recognizedvarious problems such as the following:

[0381] (1) Poor thermal stability (especially in initial annealing)

[0382] (2) Insufficient MR ratio for much more increasing reproductionsensitivity.

[0383] (3) When the free layer is a single-layered CoFe alloy layercapable of giving relatively large MR ratio, then its magnetostrictioncontrol is impossible, andgoodsoftmagnetic characteristics could not beobtained.

[0384] These problems with SV films are mentioned in detail hereunder.

[0385] (1) Thermal Stability:

[0386] As the general constitution of SV films, known is a few nmNiFe/about 1 nm Co or a few nm NiFe/about 1 nm CoFe. The SV filmstructure with such a free layer includes;

[0387] (a) 5 nanometer Ta/10 nm NiFe/1 nm Co/3 nm Cu/2 nm CoFe/7 nmIrMn/5 nanometer Ta,

[0388] (b) 5 nanometer Ta/2 nm Cu/3 nm CoFe/3 nm Cu/2 nm CoFe/7 nmIrMn/5 nanometer Ta.

[0389] After annealed at 250° C. for 4 hours or so, the MR ratio ofthose SV films decreases by about 20% or more in terms of the relativeratio based on the as-deposited films. For example, the MR ratio in theas-deposited SV film (a) is 6.4%, but, after annealed at 250° C. for 3hours, the MR ratio therein is 4.7%. Thus, the reduction in the MR ratioafter the annealing is more than 20% in terms of the relative ratiobased on the as-deposited film. The annealing step is indispensable infabrication of heads. The MR ratio in the as deposited SV film (b) nothaving a free layer of NiFe is 8.1%, but, after annealed at 250° C. for3 hours, the MR ratio therein is 6.5%. Even in the film (b), thereduction in the MR ratio after the annealing is about 20% in terms ofthe relative ratio based on the as-deposited film. At present, known isno means of preventing the MR ratio reduction without sacrificing themagnetic characteristics, or that is, any measure for improving thethermal stability for the MR ratio in SV films is not known.

[0390] For magnetic heads for high-density recording, desired are SVfilms with higher MR ratio. However, as mentioned above, the MR ratio inthe conventional SV films in the as-deposited condition is greatlylowered in thermal annealing that is indispensable to fabrication ofheads. This problem must be solved by all means for developing MR headsfor high-density recording on a level of 10 Gdpsi or more.

[0391] (2) Increase in MR Ratio by Specular Reflection:

[0392] In order to attain high MR ratio, another important matter, inaddition to the means how to keep the original MR ratio in theas-deposited condition still after thermal treatment as discussed in theprevious (1), is how to increase the peak value of the MR ratio or, eventhough the as-deposited film could not have a full-potential MR ratio,how to realize a film capable of having good MR ratio after thermaltreatment.

[0393] Regarding the GMR effect, the frequency of spin-dependentscattering increases with the increase in the number of laminated layersof magnetic layers/nonmagnetic layers in a laminate film within therange narrower than the mean free path of electrons, and the increase inthe number of laminated layers in the film brings about large MR ratioin the film. However, in the constitution of the GMR film that isactually used in practical heads, such as the constitution of SV films,there exist only the units of pinned magnetic layer/nonmagnetic spacerlayer/free layer. In general, therefore, the thickness of the GMR filmincluding SV films is smaller than the mean free path of electrons,which is against the MR ratio increase to which the invention isdirected.

[0394] In order to overcome this problem as much as possible, the numberof the layers constituting the GMR film may be increased. One example ofsuch GMR film constitution known in the art is a dual-spin valve film(or a symmetry spin valve, hereinafter referred to as D-SV film) inwhich the pinned magnetic layer is of a two-layered film composed ofupper and lower layers and the upper and lower layers are separated by afree layer existing therebetween. This will be helpful in solving theproblem, but at least at present could not solve all problems withpracticable SV films. For example, in the D-SV film where the free layeris subbed with a nonmagnetic spacer layer, it is difficult to make thefree layer have completely satisfactory soft magnetic characteristicscharacteristics with respect to, for example, the anisotropy field Hkand the level of magnetostriction λ. In addition, where the two upperand lower pinned magnetic layers are used, it is desirable that the twoantiferromagnetic films for pinning the magnetization of those twolayers have the same blocking temperature. In fact, however, it isdifficult to make the lower antiferromagnetic film, which is positionedin the lower side, and the upper antiferromagnetic film, which ispositioned in the upper side via a nonmagnetic spacer layer and a freelayer, have the same characteristics. Therefore, from the viewpoint ofthe MR ratio, the D-SV film is preferred, but from the viewpoint ofpractical applications, it still has many problems to be solved.

[0395] Given that situation, improving the characteristics of thepopular SV film having one antiferromagnetic film is being muchinvestigated. One means for the improvement is to incorporate mirrorreflectivity into the film. This is to dispose a reflective film on oneor both sides of the basic unit of the GMR film of magneticlayer/nonmagnetic spacer layer/magnetic layer, so that electrons areelastically reflected on the reflective film to thereby prolong the meanfree path of electrons in the basic unit of the GMR film.

[0396] On the upper and lower layers of the basic unit of theconventional GMR film, electrons are scattered non-elastically. In thatunit, therefore, electrons could not move to the length of the mean freepath intrinsic to them, and they could not enjoy the spin-dependentscattering over the thickness of the basic unit of the GMR film. As aresult, the MR ratio in the film could not be increased to a desireddegree. Contrary to this, if the GMR structure has upper and lowerlayers with ideal surface reflectivity, the basic unit of the GMR filmcould be apparently equivalent to the constitution of an infiniteartificial lattice film, in which electrons could scatterspin-dependently to the length comparable to their mean free path. As aresult, the MR ratio in thisGMR constitution could increase. Thereflective films to be disposed over the upper and lower magnetic layeron the nonmagnetic spacer layer may be or even may not be spin-dependentones. Even the latter spin-independent reflective films could fullyexhibit the intended effect.

[0397] The effect applies not only to ordinary SV film structures butalso to D-SV film structures. However, the reflective films would beineffective in artificial lattice films which naturally comprises anumerous and unlimited number of layers and in which electrons arenaturally scattered in a spin-dependent manner to the length of theirintrinsic mean free path. The specular reflection effect is greater inSV film structures comprising a small number of constituent layers.

[0398] Some SV films have heretofore been proposed, which positivelyincorporate the specular reflection noted above. The following areexamples of those SV films.

[0399] (c) Si substrate/5 nm NiO/2.5 nm Co/1.8 nm Cu/4 nm Co/1.8 nmCu/2.5 nm Co/50 nm NiO,

[0400] (d) Si substrate/50 nm NiO/2.5 nm Co/2 nm Cu/3 nm Co/0.4 nm Au(Ref.; J. R. Jody et al., IEEE Mag. 33, No. 5, 3580 (1997)),

[0401] (e) MgO substrate/10 nm Pt/5 nm Cu/5 nm NiFe/2.8 nm Cu/5 nmCo/1.2 nm Cu/3 nmAg (Ref.; Y. Kawabu et al., Summary of Reports inSpring Meeting in 1997, p. 142, by the Japan Metal Society),

[0402] (f) Si substrate/200 nm Si₃N₄/20 nm Bi₂O₃/4 nm Au/4 nm NiFe/3.5nm Cu/4 nm CoFe (Ref.; D. Wang et al., IEEE Mag. 32, No. 5, 4278(1996)).

[0403] In those SV film structures, the underlined parts are thoseconsidered as specular reflection films.

[0404] In the SV film (c), the upper and lower specular reflection filmsare of an oxide. Simply, it is considered that insulating oxides havinga high potential barrier are more effective than metals for electronwave reflection, as having higher mirror-reflectivity. In addition,since the NiO film is not only a reflective oxide film but also anantiferromagnetic film, it further acts to spin the magnetization of themagnetic layer adjacent to NiO. The above are D-SV films. It is believedthat even normal SV films, reversal SV films and others having asingle-layered antiferromagnetic film could enjoy the specularreflection on one side. However, these have some disadvantages and arenot practicable in the current stage.

[0405] First, Nio has low magnetic coupling force and its practicabilityis low. This is because, in a weak magnetic coupling field, themagnetization direction of the pinned magnetic layer is unstable owingto the stray magnetic field from the recording media, and the outputwill fluctuate. In addition, irrespective of Nio and any other oxidesfor a cap layer, the contact resistance between the lead electrodes andthe upper oxide layer is large. The increase in the contact resistanceis unfavorable, as often causing ESD (electrostatic discharge). Inaddition, where CoFe is used as the free layer, it is understood thatthe CoFe layer could not exhibit soft magnetic characteristics if notoriented in fcc(111). Where the free layer is positioned in the lowerside, a subbing oxide layer, if used, for the free layer shall not workwell as a buffer layer for fcc(111)-orientation buffer for CoFe. Withthat constitution, the SV film could not have soft magneticcharacteristics.

[0406] In the SV film (d), the underlayer of NiO is an antiferromagneticfilm additionally acting for specular reflection, and the top Au layeris a reflective film. Also in the SV film (e), the top Ag film is areflective film. In (e), the potential difference between the Ag filmand the film surface induces specular reflection. Thereason why thenoblemetal film of Au or Ag is effective as the surface reflective film isnot clear. One reason is written in the reference for (d), in which theysay that, since the surface diffusion of noble metal films is higherthan that of transition metal films, the surface planarity of noblemetal films is higher than that of transition metals, and thereforenoble metal films will be ready to exhibit surface reflection.

[0407] The reflective films of metals are superior to those of oxides,as the former are free from the problem of contact resistance with leadelectrodes, which problem, however, is inevitable in the latter.However, the mirror reflectivity of noble metal films of Au or Ag isoften lost in practical devices. This is because, in practical MRdevices or MR heads, the SV film is rarely exposed outside but isusually covered with any other additional film.

[0408] For example, in shielded MR heads, an upper magnetic gap film ofalumina or the like is laminated on the SV film. As so written in thereference for (d), the specular reflection is much influenced by thesurface or interface condition. Therefore, if any additional film isprovided over the surface of the specular reflection film, the mirrorreflectivity of the film shall naturally be varied by the overlyingadditional film. The film structure in which the MR characteristics ofthe SV film are varied by the additional film that overlies the SV filmis problematic in its practical applications.

[0409] In fact, it is reported that, when a Ta film which is generallyused as a protective film is laminated on the surface of the Au film inan SV film, then the Au film loses its mirror reflectivity. Accordingly,SV films utilizing the mirror reflectivity on their surface often losetheir effect in device structures that are directed to practicalapplications, and are therefore not practicable.

[0410] The SV film (f) incorporates the Au film as the specularreflection film, like in (d). In (f), however, the Au film does notexhibit the reflective effect on its surface, but induces themirror-reflective effect in the interface between the metal films. Inthis connection, it is understood that, when the Au film is directlyformed on a substrate in the absence of a suitable underlayertherebetween, it often grows in islands. In order to prevent this, aparticular underlayer is provided between the Au film and the substratein (f). Above the underlayer, the smoothness of the Au film formed isenhanced as much as possible so as to ensure a sharp interface betweenthe Au film and the overlying NiFe film.

[0411] However, the underlayer in (f) is not practicable. Briefly, inproducing (f), an Au film is formed on the subbing Bi₂O₃ film having athickness of 20 nanometers. This is to utilize the fact that the Au filmformed on the subbing Bi₂O₃ film exhibits good reflectivity after it isannealed at 350° C. (Ref.; C.R. Tellier and A.J. Tosser, Size Ellects inThin Films, Chapter I, Elsevier, 1982; L.I. Maissel et al., Handbook ofThin Film Technology, McGraw-Hill Publishing Company, 1983).

[0412] In addition, another underlayer of Si₃N₄ film having a thicknessof 200 nanometers is provided below the Bi₂O₃ film. In other words, thetwo-layered underlayer having a total thickness of 220 nanometers isformed below the Au film, which is then annealed at a high temperatureof 350° C. The thick underlayer having a thickness of 220 nanometers isextremely disadvantageous for narrow gaps that shall be much morenarrowed for the coming, high-density recording systems, and will bealmost impracticable. In addition, the high-temperature thermaltreatment at 350° C. will cause interfacial diffusion at the interfaceof magnetic layer/nonmagnetic spacer layer, thereby disturbing thespin-dependent scattering of electrons which is intrinsic andindispensable to GMR films. As a result, the MR ratio in the film willbe greatly lowered. The thermal treatment temperature for the film (f)will cause interfacial scattering even in other SV films thatincorporate a laminate film of Co(CoFe) /Cu/Cu(CoFe) having good thermalstability.

[0413] (3) Magnetostriction Control in CoFe:

[0414] Where a CoFe layer is used as a free layer, it is understood thatan fcc (111) -oriented underlayer may be applied thereto so as to inducefcc(111) orientation of the CoFe layer, whereby the soft magneticcharacteristics of the CoFe layer is improved. As the fcc(111)-orientedunderlayer, used is a Cu layer or an Au layer. However, we, theinventors have found that, in the conventional technique, themagnetostriction which is another important factor of soft magneticcharacteristics is not controlled at all, and that the thermal stabilityof the CoFe layer much depends on the underlayer. For example, the SVfilms based on the published patent specification noted above includethe following:

[0415] (g) 5 nanometer Ta/2 nm Cu/2 nm CoFe/3 nm Cu/2 nm CoFe/7 nmIrMn/5 nanometer Ta,

[0416] (h) 5 nanometer Ta/2 nm Au/3 nm CoFe/3 nm Cu/2 nm CoFe/7 nmIrMn/5 nanometer Ta.

[0417] In the film (g), the Cu layer is oriented in fcc(111), and theCoFe layer above the fcc (111)-oriented Cu layer is also oriented infcc(111) to exhibit soft magnetic characteristics. However, the film (g)is problematic in that (i) its thermal stability is poor (the MR ratioin the as-deposited film of 8.1% is decreased to 6.5% after thermaltreatment at 250° C. for 4 hours, and the MR ratio reduction in theheat-treated film is 20% in terms of the relative ratio), and (ii) themagnetostriction λ is −14×10⁻⁷, and its peak value is large. Thus, thefilm (g) is not always practicable. Regarding the magnetostriction λ,there is no definite standard in the art. As one standard, the preferredrange of the magnetostriction λ will fall between −10×10⁻⁷ and +10×10⁻⁷or so.

[0418] In addition, even when Au is used as the fcc material in place ofCu (as in the film (h)), the film is still problematic in that (i) itsthermal stability is poor (the MR ratio in the as-deposited film of 8.4%is decreased to 6.5% after thermal treatment at 250° C. for 4 hours, andthe MR ratio reduction in the heat-treated film is 23% in terms of therelative ratio), and (ii) the magnetostriction λ is +33×10⁻⁷, and itspeak value is large. Thus, like that with a Cu layer, the film is stillnot always practicable.

[0419] XRD patterns of the spin valve films (g) and (h) are obtainedthrough θ -2θ scanning, and studied. In those patterns, the three layersof CoFe/Cu/CoFe had nearly the same d spacing value and gave one peak.This one peak is referred to herein. The fcc-oriented d-(111) spacing inthe three layers CoFe/Cu/CoFe above Cu is 2.054 nanometers; and thefcc-oriented d-(111) spacing in the three layers CoFe/Cu/CoFe above Auis 2.086 nanometers. As will be mentioned hereunder, at the intermediateof the d-(111) spacing above Cu and Au, the magnetostriction in thefilms could be suitably controlled and reduced. Therefore, it has beenfound that the too small d-(111) spacing above Cu and the too larged-(111) spacing above Au are both unfavorable.

[0420] As mentioned above, it has been found that forming the free layerof CoFe on the merely fcc(111)-oriented underlayer is unsatisfactory inpoint of magnetostriction control. For reducing the magnetostriction,employable is a structure where CoFe is formed on an fcc(111)-orientedNi₈₀Fe₂₀ at around zero magnetostriction level so that the entire freelayer is made to have zero magnetostriction owing to that NiFe havingnearly zero magnetostriction (e.g., the constitution (a) noted above).However, as so mentioned hereinabove, this structure is stillproblematic in that its MR characteristic is still degraded in thermaltreatment.

[0421] As mentioned above, the MR ratio reduction in conventional spinvalve films after thermal treatment is great, and the improvement in thethermal stability of the films is desired.

[0422] As one measure for increasing the MR ratio in spin valve films,specular reflection is widely noticed. However, the reflective film inconventional spin valve films is of an insulating material such asoxides, etc. In addition, some conventional spin valve films utilize thereflectivity on their surface. Therefore, the conventional spin valvefilms of those types often induce ESD, for example, owing to theincrease in the contact resistance with lead electrodes, or protectivefilms, if formed on the spin valve films, cancel the mirror reflectivityof the films. Thus, the conventional spin valve films have such variousproblems in their practical applications. Apart from those, anothertechnique of utilizing interfacial specular reflection is beinginvestigated. However, this requires a specific underlayer. Therefore,spin valve films utilizing such interfacial specular reflection arepoorly practicable. For these reasons and in consideration of thepractical applicability of spin valve films to devices and magneticheads, it is desirable that the MR ratio in spin valve films isincreased by specular reflection.

[0423] In addition, for improving the soft magnetic characteristics ofspin valve films, it is desired to control and reduce themagnetostriction in Co-based magnetic layers of CoFe alloys or the like.

[0424] In particular, the mirror reflectivity of spin valve films toincrease the MR ratio in the films and to reduce the magnetostrictiontherein must not be degraded in thermal treatment for ensuring thepractical application of the films.

[0425] This embodiment of the invention is to solve the problems notedabove, and its object is to provide a magnetoresistance effect device inwhich the MR characteristic of the spin valve film is prevented frombeing degraded in thermal treatment, and to provide a magnetoresistanceeffect device in which the MR ratio in the spin valve film is increasedby specular reflection in consideration of its practical applications,in which the magnetostriction in the spin valve film is reduced, and inwhich the MR ratio reduction and the magnetostriction increase in thespin valve film in thermal treatment are both retarded. Another objectis to provide a magnetic head and a magnetic recording/reproducingsystem incorporating the magnetoresistance effect device and thereforehaving improved recording/reproducing characteristics and improvedpractical applicability.

[0426] The embodiment to solve the problems noted above is describedbelow with reference to the accompanying drawings.

[0427]FIG. 32 is a sectional view of the essential structure of oneembodiment of the magnetoresistance effect device (MR device) of theinvention. In FIG. 32, 1 is a first magnetic layer, and 2 is a secondmagnetic layer. These first and second magnetic layers 1 and 2 arelaminated via a nonmagnetic spacer layer 3 existing therebetween. Thesefirst and second magnetic layers 1 and 2 are not antiferromagneticallycoupled to each other, but form a non-coupled, laminated magnetic film.

[0428] The first and second magnetic layers 1 and 2 may be made of aCo-containing ferromagnetic material of, for example, simple Co or a Coalloy. The magnetic layers 1 and 2 may also be made of an NiFe alloy orthe like. Of those materials, especially preferred is a Co alloy asbeing able to enlarge both the bulk effect and the interfacial effect,whereby the MR ratio in the MR device could be enlarged.

[0429] The Co alloy for constituting the magnetic layers 1 and 2includes Co-based alloys containing at least one or more elementsselected from Fe, Ni, Au, Ag, Cu, Pd, Pt, Ir, Rh, Ru, Os, Hf, etc. It isdesirable that the additive element content of the alloys falls between5 and 50 at. %, more preferably between 8and 20 at. %. This is because,if the additive element content is too small, the bulk effect of thealloys will be poor; but, on the contrary, if the additive elementcontent is too large, the interfacial effect of the alloys will lower.Of the additive elements, especially preferred is Fe, as giving large MRratio.

[0430] Of the first and second magnetic layers 1 and 2, the lower firstmagnetic layer 1 is formed on a magnetoresistance effect-improving layer(MR-improving layer) 4. The MR-improving layer 4 is formed on anonmagnetic layer having a subbing function (hereinafter referred to asnonmagnetic underlayer) 5. The nonmagnetic underlayer 5 is, for example,a layer containing at least one element selected from Ta, Ti, Zr, W, Cr,Nb, Mo, Hf and Al, for which are used any of simple metals or alloys ofthose metals, or compounds such as oxides or nitrides of those metals.Where the nonmagnetic underlayer 5 is of an oxide of Ta or the like,electrons that could not be reflected on the MR-improving layer 4 couldbe reflected on the interface of nonmagnetic underlayer 5/MR-improvinglayer 4, as will be described in detail hereunder.

[0431] The first magnetic layer 1 is a free layer of which themagnetization direction varies depending an applied magnetic field. Onthe second magnetic layer 2, formed is an antiferromagnetic layer 6 ofany of IrMn, NiMn, PtMn, FeMn, RuRhMn, PdPtMn or the like. From theantiferromagnetic layer 6, abias magnetic field is applied to the secondmagnetic layer 2, by which the magnetization of the layer 2 is pinned.Accordingly, the second magnetic layer 2 is a pinned magnetic layer.

[0432] Apart from the method of pinning the second magnetic layer notedabove in which the second magnetic layer is directly contacted with theantiferromagnetic layer for thereby pinning its magnetization direction,a so-called Synthetic antiferromagnetic structure may also be employedfor the intended pinning, though not shown in FIG. 32. Briefly, a thirdmagnetic layer is laminated on the second magnetic layer via a layer ofRu, Cr or the like, and the second magnetic layer and the third magneticlayer are antiferromagnetically coupled to each other in a manner ofRKKY. Using the Synthetic antiferromagnetic structure is preferred, asthe bias point is stabilized and the stability of the pinningcharacteristic at high temperatures is enhanced. Concretely, examples ofthe structure comprising the second magnetic layer and the thirdmagnetic layer include CoFe/Ru/CoFe, Co/Ru/Co, CoFe/Cr/CoFe, Co/Cr/Co,etc. The antiferromagnetic layers to be applied to the Syntheticantiferromagnetic structure may be the same as those mentioned above.

[0433] Examples of the material that constitutes the nonmagnetic layer 3to be disposed between the first and second magnetic layers 1 and 2include Cu, Au, Ag and their alloys; paramagnetic alloys comprising anyof these metals and magnetic elements; and Pd, Pt and alloys consistingessentially of these.

[0434] On the antiferromagnetic layer 6, formed is a protective layer 7.The protective layer 7 maybe made of metals or alloys which are the sameas those for the nonmagnetic underlayer 5. These constituent layers formthe spin valve film 8 of this embodiment. A pair of electrodes (notshown) for supplying sense current are connected to the spin valve film8 to construct a spin valve GMR device. The spin valve GMR device may beprovided with a bias magnetic field-applying film of a hard magneticfilm or an antiferromagnetic film, which is to apply a bias magneticfield to the free layer . In this case, it is desirable that the biasmagnetic field is applied in the direction nearly perpendicular to themagnetization direction of the pinned magnetic layer 2. In FIG. 32, 9 isa substrate.

[0435] Of the layers constituting the spin valve film 8 noted above, theMR-improving layer 4 is the characteristic part of the invention. TheMR-improving layer 4 in FIG. 32 is of a laminate film comprising a firstmetal film 4 a and a second metal film 4 b. The metal films 4 a and 4 bfunction as underlayers for the spin valve film 8, and these may containat least one element selected from Cu, Au, Ag, Pt, Rh, Ru, Al, Ti, Zr,Hf, Pd and Ir.

[0436] Of those plural metal films, the essential element constitutingthe first metal film 4 a that is adjacent to the first magnetic layer(free layer) 1 does not form solid solution with the essential elementconstituting the free layer 1. Preferably, the same shall apply also tothe second metal film 4 b. Specifically, it is desirable that theessential element constituting the second metal film 4 b does not formsolid solution with the essential element constituting the free layer 1.In particular, the essential elements each constituting those first andsecond metal films 4 a and 4 b may not form solid solution with eachother. It is further desirable that the first metal film 4 a to beadjacent to the free layer 1 is of a metal having a short electronwavelength, while the second metal film 4 b adjacent to the first metalfilm 4 a is of a metal having a longer electron wavelength (than that ofthe metal constituting the first metal film 1 a).

[0437] The definition “not forming solid solution” as referred to hereinis explained. For two different elements A and B, the condition in whichone element A does not form solid solution with another element B (forthe terminology “not forming solid solution”) is meant to indicate thefollowing condition: In a binary phase diagram (for example, see BinaryAlloy Phase Diagram, 2nd edition, ASM International, 1990, etc.), whenthe amount by at. % of B capable of dissolving in a matrix of A to formsolid solution at low temperatures around room temperature or so, andthe amount by at. % of A capable of dissolving in a matrix B to formsolid solution at such low temperatures are both at most 10%, thecombination of those elements A and B is in the condition of “notforming solid solution”.

[0438] Concretely mentioned are a case where the magnetic layer (forexample, the free layer 1) is of Co or a Co alloy, and a case where themagnetic layer is of an Ni alloy. Since the subbing film is preferablyof an fcc metal or an hcp metal for attaining the fcc orientation in themagnetic layer, the element constituting the MR-improving layer that isadjacent to the magnetic layer will be selected from Al, Ti, Cu, Zr, Ru,Rh, Pd, Ag, Hf, Ir, Pt, Au, etc. Of those elements, three elements ofCu, Ag and Au satisfy the requirement of not forming solid solution withCo. On the other hand, three elements of Ru, Ag and Au satisfy therequirement of not forming solid solution with Ni. For the magneticlayer of an Ni alloy, Cu will form solid solution with the Ni alloy fromthe relation of the two, Cu and Ni in the phase diagram. However, thepresent inventors' experiments have revealed the fact that, when Cu isused in the MR-improving layer, it forms less solid solution with Ni inthe neighboring magnetic layer. Specifically, on the basis of theexperimental data mentioned below, it is decided that an Ni alloy and Cudo not form solid solution with each other.

[0439] When the free layer is thin, the MR-improving layer acts as thenonmagnetic high-conductivity layer in the first embodiment mentionedhereinabove. However, once the interface between the nonmagnetichigh-conductivity layer and the free layer has become diffusive owing toelectron diffusion in that interface, the electron transmittance fromthe free layer to the nonmagnetic high-conductivity layer is lowered. Inother words, even when the magnetization direction of the pinned layeris parallel to that of the free layer, the diffusive interface receivesnon-elastic electron scattering so that the mean free path of electronsfor up-spin could not be prolonged. As a result, this induces MR ratiodepression. This phenomenon is seen when the ultra-thin free layer formssolid solution with the nonmagnetic high-conductivity layer, and becomesmore remarkable in thermal treatment. Accordingly, the MR ratiodecreases after thermal treatment. To confirm this phenomenon, we, thepresent inventors made one experiment in which Cu is attached to an Nialloy layer. In that experiment, less MR ratio depression was seen.

[0440] From the experimental results noted above, it is decided that Nialloys do not form solid solution with Cu. Accordingly, Cu could be inthe group of elements not forming solid solution with Ni alloys. Forthese reasons, in the invention, the group of elements not forming solidsolution with Ni alloys shall include Cu in addition to the elements tobe derived from the phase diagram. Concretely, the group includes Ru,Ag, Au and Cu. With any of those elements being disposed adjacent to themagnetic layer which does not form solid solution with any of thoseelements, the compositional steepness in the interface between themagnetic layer and the MR-improving layer is not lost in thermaltreatment and good specular reflection could be expected.

[0441] The premise in this case is that the magnetic layer isfcc-oriented, which, however, is not imitative. Needless-to-say, themagnetic layer may be non-oriented or may have a microcrystallinestructure, and the MR-improving layer may be applied to the magneticlayer of that type. Concretely, the magnetic layer may be any ofamorphous magnetic layers or microcrystalline-structured magnetic layersof CoFeB, CoZrNb or Cr to which may be added any of Ti, Zr, Nb, Hf, Mo,Ta or the like.

[0442] In the invention, the MR-improving layer comprising the elementsnoted above may be partly in the form of a laminate film with any othermetal films or of an alloy film with any other elements for the purposeof more ensuring the d-spacing control in the layer and themicrocrystalline structure of the layer. The elements constituting themetal films to form the laminate film are desirably fcc metals and hcpmetals, including, for example, Al, Ti, Cu, Zr, Ru, Rh, Pd, Ag, Hf, Ir,Pt, Au, etc.

[0443] Where the MR-improving layer is of a laminate film, metals of themetal films constituting it and not to be adjacent to the magnetic layermay be capable of forming solid solution with the metals of the othermetal films to adjacent to the magnetic layer.

[0444] Examples of using a laminate film for the MR-improving layer 4are mentioned below. Where the magnetic layer 1 is of Co or a Co alloyand the metal film 4 a is of Cu not forming solid solution with theelement(s) of the layer 1, it is possible that the metal film 4 bcomprises at least one element selected from Al, Au, Pt, Rh, Pd and Irall capable of forming solid solution with Cu. Where the metal film 4 ais of Ag, the metal film 4 b may comprise at least one selected from Pt,Pd and Au. Where the metal film 4 a is of Au, the metal film 4 b maycomprise at least one selected from Pt, Pd, Ag and Al. Where themagnetic layer 1 is of an Ni alloy and the metal film 4 a is of Ru notforming solid solution with the elements of the layer 1, it is possiblethat the metal film 4 b comprises at least one element selected from Rh,Ir and Pt all capable of forming solid solution with Ru. To Ag and Aufor the film 4 b, the same as above for the metal film 4 a of Cu couldapply.

[0445] Of the combinations noted above, it is desirable that the twoelements constituting the MR-improving layer 4 could form solid solutionto a level of at least 10%. For example, preferred are combinations ofAu—Cu, Ag—Pt, Au—Pd, Pt—Cu, Au—Ag, etc. Regarding the combination of themetal film 4 a and the metal film 4 b, however, it is not alwaysnecessary that the two can form solid solution in some degree. Forexample, combinations of Cu—Ru, Cu—Ag and the like are also employableherein. The laminate film for the MR-improving layer 4 is not limited toonly the two-layered laminate film composed of the first metal film 4 aand the second metal film 4 b, but may be composed of three or morelayers.

[0446] The MR-improving layer 4 is not limited to the laminate filmcomposed of the first metal layer 4 a and the second metal layer 4 b.For example, as in FIG. 33, the MR-improving layer 4 may be an alloylayer 4 c that comprises elements not forming solid solution with theessential components constituting the magnetic layer 1. To the alloylayer 4 c in this case, the same as above for the laminate film couldapply. Concretely, for example, where the magnetic layer 1 is of Co or aCo alloy, the alloy layer 4 c comprises, as the essential constituentelement, at least one selected from three elements of Cu, Ag and Au.Where the magnetic layer 1 is of an Ni alloy, the alloy layer 4 ccomprises, as the essential constituent element, at least one selectedfrom four elements of Ru, Ag, Au and Cu.

[0447] The alloy layer 4 c may comprise at least one additional elementin addition to the essential constituent elements noted above. As theadditional elements, used are elements capable of forming solid solutionwith the essential constituent elements of the alloy layer 4 c so as toprevent phase separation in the layer 4 c. For example, when theessential constituent element of the alloy layer 4 c is Cu, the alloyfor the layer 4 c shall contain a noble metal, including, for example,Cu—Au, Cu—Pt, Cu—Rh, Cu—Pd, Cu—Ir, etc. When the essential constituentelement of the alloy layer 4 c is Ag, the alloy for the layer 4 c may bea noble metal alloy, including, for example, Ag—Pt, Ag—Pd, Ag—Au, etc.When the essential constituent element of the alloy 4 c is Au, the alloyfor the layer 4 c may also be a noble metal alloy, including, forexample, Au—Pt, Au—Pd, Au—Ag, Au—Al, etc.

[0448] Of the alloys noted above, it is desirable that the two elementsconstituting the alloy layer 4 c for the MR-improving layer 4 could formsolid solution to a level of at least 10%. For example, preferred arealloys of Au—Cu, Ag—Pt, Au—Pd, Au—Ag, etc. As mentioned above, varioustypes of morphology could apply to the MR-improving layer 4. Forexample, the MR-improving layer 4 may also be a laminate film composedof the metal film 4 a and the alloy layer 4 c, as in FIG. 34.

[0449] Where the free layer 1 is of a Co-based magnetic material, it isdesirable that the MR-improving layer 4 which acts as the underlayer forthe free layer 1 is of a metallic material having the same fcc-crystalstructure as the Co-based magnetic material has, or of an hcp-structuredmetallic material capable of readily orienting the overlying film infcc-orientation. In view of those points, Cu, Au, Ag, Pt, Rh, Pd, Al,Ti, Zr, Hf, Ir and their alloys such as those mentioned above arepreferable materials for constituting the MR-improving layer 4. Further,when the MR-improving layer 4 is of a laminate film or an alloy layer ofthose metals, it is effective for reducing the magnetostriction in thefree layer 1 of a Co-based magnetic material such as Co-Fe alloys, etc.,as will be described in detail hereunder.

[0450] It is desirable that the thickness of the MR-improving layer 4 isat least 2 nanometers, in order that the layer 4 could have the functionas a underlayer. However, if too thick, the layer 4 will increase theshunt current flow to thereby reduce the MR ratio in the film 8.Therefore, it is desirable that the thickness of the MR-improving layer4 is at most 10 nanometers, more preferably at most 5 nanometers.

[0451] The MR-improving layer 4 has the function of improving thethermal stability of the spin valve film 8, the function as a specularreflection film (interfacial reflection film) in the spin valve film 8,the function of still keeping high MR ratio even if the free layer isthin, the function of reducing the magnetostriction in the free layer 1of a Co-based magnetic material, and the function of controlling themicrocrystalline structure of the spin valve film 8. Based on thosefunction, the MR-improving layer 4 improves the MR characteristics ofthe spin valve film 8. The functions of the MR-improving layer 4 aredescribed in detail hereunder.

[0452] First referred to is the process of thermal degradation of spinvalve films. One reason for the thermal degradation of the MRcharacteristics of spin valve films during annealing is that thespecular reflection on the sides of the magnetic layers 1 and 2 notcontacted with the nonmagnetic spacer layer 3 will vary duringannealing. FIG. 35A to FIG. 35C show the reduction in the MR ratio inspin valve films after thermal treatment. In those, IFs indicates theinterface with spin-dependent scattering thereon, and IFM indicates withno spin-dependent scattering but with specular reflection scatteringthereon. Precisely, FIG. 35A and FIG. 35B schematically show an idealcondition (this corresponds to the as-deposited condition); and FIG. 35Cschematically shows the condition after annealing.

[0453] As in FIG. 35A and FIG. 35B, specular reflection scatteringoccurs on the both sides of the three-layered laminate structure, freelayer 1/nonmagnetic spacer layer 2/pinned magnetic layer 3, of the basicunit of the spin valve GMR in the as-deposited condition (even thoughthe interface is between metal films). However, as in FIG. 35C, in thesystem that readily forms solid solution in a process of annealing,interfacial diffusion occurs, or that is, the interface becomesdiffusive to lower its mirror-reflectivity after annealing. As a result,it is considered that, in that system, the MR characteristics aredegraded in thermal treatment.

[0454] Few reports are found relating to the specular reflection on theinterface between metal films, and any positive proof of the specularreflection on that interface has not been well established as yet.However, as will be mentioned hereunder, even on the interface betweenmetal films with small potential difference therebetween, some idealspecular reflection will occur. For example, specular reflection occurson the interface of NiFe/CoFe in the as-deposited condition in whichmixing of the two is relatively small. However, after the system ofNiFe—CoFe is annealed, interfacial diffusion occurs readily on thatinterface of NiFe/CoFe where the components will form solid solution,whereby the compositional steepness in the interface will be lost. As aresult, it is considered that the MR ratio will lower in that systemafter thermal treatment.

[0455] Concretely, in a spin valve film incorporating a free layer of alaminate film of NiFe/CoFe, the specular reflection on the NiFe/CoFeinterface is lost in annealing. As a result, for example, the MR ratioof 7.3% in the as-deposited film is lowered to 5.8% after annealing at250° C. for 4 hours. One reason for this will be because the specularreflection coefficient at the NiFe/CoFe interface would be varied inannealing, whereby the MR ratio in the film would be also varied afterannealing.

[0456] In the prior art technology, the interfacial specular reflectionhas not been taken into consideration since the NiFe/CoFe interface isthe interface between metal films and since the two, NiFe and CoFe arein nearly the same electron condition. In the as-deposited condition,the interface could be uniform with relatively low-level mixing ofelements thereon, and therefore specular reflection will occur even onthe metal film interface of that type. However, since the NiFe/CoFesystem forms solid solution in its interface, the interface will readilydiffuse and mix when annealed, whereby the compositional steepness inthe interface will be lost and the specular reflection coefficient therein will become small. As a result, the MR characteristics in the systemwill be degraded. In a different aspect, this means that the MR ratio inthe as-deposited film is larger by the degree of specular reflectionthan that in the annealed film.

[0457] When the free layer is thin and MR-improving layer is disposed tothe free layer, the MR-improving layer acts as the nonmagnetichigh-conductivity layer in the first embodiment mentioned hereinabove.However, once the interface between the nonmagnetic high-conductivitylayer and the free layer has become diffusive owing to atomic diffusionin that interface, the electron transmittance from the free layer to thenonmagnetic high-conductivity layer is lowered. In other words, evenwhen the magnetization direction of the pinned layer is parallel to thatof the free layer, the diffusive interface receives non-elastic electronscattering so that the mean free path of electrons for up-spin could notbe prolonged. As a result, this induces MR ratio depression. Thisphenomenon is seen when the ultra-thin free layer forms solid solutionwith the nonmagnetic high-conductivity layer, and becomes moreremarkable in thermal treatment. Accordingly, the MR ratio decreasesafter thermal treatment.

[0458] It is important to form a stable interface between the free layerand the nonmagnetic high-conductivity layer, which does not interferewith the up-spin transmission even after thermal treatment. Concretely,it is important that the material of the free layer does not form solidsolution with the material of the nonmagnetic high-conductivity layer.For example, when the magnetic layer is of a Co alloy, then thenonmagnetic high-conductivity layer may be any of Cu, Au, and.

[0459] In view of the above, as one means of really preventing the MRcharacteristic degradation, it is important to dispose a metal materialwhich does not form solid solution with the materials of the magneticlayers 1 and 2, at the both sides of the basic unit of the GMR film. Inaddition, for example, when a material of CoFe alloys and the like isused in forming the basic GMR unit, the insoluble metal material layerof that type must have an additional function as a seed layer capable oforienting the CoFe alloy layer in fcc(111)orientation. Therefore, it isunderstood that metal materials capable of readily orienting in fcc(111)orientation are preferred for the additional metal layers. Moreover,when the free layer is of a CoFe alloy, magnetostriction control in thelayer is also important.

[0460] Another factor of the MR characteristic degradation in spin valvefilms in annealing is the change in the microstructure of the films inthermal treatment. The microstructure of spin valve films is oneimportant factor for improving the thermal stability of the films. Forthis, the microstructure of the films is desirably such that, in thebasic GMR unit of free layer/nonmagnetic spacer layer/pinned magneticlayer, all interposing interfaces and the both outer interfaces could bekept stable even after thermal annealing. This is because the interfacebetween free layer/nonmagnetic spacer layer and that between nonmagneticspacer layer/pinned magnetic layer are both important for ensuringstrong, spin-dependent interfacial scattering thereon, and because theboth outer interfaces of the two magnetic layers are also important forthermally stabilizing the spin-independent specular reflectionscattering thereon. Where the magnetic layers are of laminate films, theinterface between the constituent magnetic films, one being adjacent tothe nonmagnetic spacer layer while the other being adjacent to that one,shall be the specular reflection interface for spin-independentscattering thereon.

[0461] In order to realize the condition noted above, it is naturallydesirable that the materials for magnetic layer/nonmagnetic layer are soselected that the material of the magnetic layer does not form solidsolution with that of the nonmagnetic layer (for example, CoFe/Cu, orCo/Cu). On the interface of that type, the two materials do not formsolid solution. Therefore, it is important to prevent atomic diffusionon the interface of magnetic layer/nonmagnetic layer and on the outerinterface of the magnetic layer not adjacent to the nonmagnetic spacerlayer. For this, ideally, it is desirable that the crystals in the basicGMR unit moiety are single crystals. (In this connection, in one exampleof CoFe/Cu/CoFe, the constituent crystals do not differ so much in thelattice constant, and the crystal grains do not separately exist in eachlayer but form aggregated grains in the integrated constitution ofCoFe/Cu/CoFe.) In fact, however, in the spin valve film 8 as formed onan amorphous layer of, for example, alumina or the like, single crystalsare difficult to form.

[0462] Therefore, for practicable and realizable crystal structures,preferred are so-called pseudo-single-crystal film structures in whichthe intergranular boundaries, if any are not ordinary intergranularboundaries but are so-called sub-grain boundaries with little in-planeorientation gap. In the invention incorporating the MR-improving layer 4noted above, spin valve films having small angle tilt boundaries ofsub-grain boundaries are obtained and their reproducibility is high.Concretely, the spin valve films of the invention can be oriented infcc(111) orientation, and the in-plane shift of the crystal orientationin the intergranular boundaries in the films could be limited within 30degrees. The magnetoresistance effect characteristics of the spin valvefilms of the invention are greatly improved owing to the grain controlin the films The crystal structures of the films will be described indetail hereunder.

[0463] Where the magnetization of the spin valve film is pinned with anMn-based ferromagnetic layer, for example, as in CoFe/Cu/CoFe/IrMn, theMR characteristics of the film will be greatly degraded if Mn passesthrough the intergranular boundaries therein to penetrate through theCoFe layer and diffuses even into the Cu layer. Therefore, in theconstitution of CoFe/Cu/CoFe/IrMn or the like, it is desirable that Mnis prevented from passing through the intergranular boundaries todiffuse into the Cu layer. On the other hand, since the interface of themagnetic layer not adjacent to the nonmagnetic spacer layer shall be theinterface to induce specular reflection, the microstructure of the spinvalve film is preferably such that the interface of the magnetic layeris difficult to disorder. For this, it is important that the material ofthe layer positioned outside of the ferromagnetic layer does not formsolid solution with the essential constituent element of the magneticlayer.

[0464] In the case where the antiferromagnetic layer is of IrMn or thelike in which the lattice spacing greatly differs from that in CoFe,significant lattice distortion occurs between the CoFe layer and theoverlying IrMn layer. If so, atomic dislocation will occur in theinterface of CoFe/IrMn to relieve the lattice distortion therein. Forpreventing such an unfavorable interfacial phenomenon, for example, anadditional layer capable of stabilizing the lattice spacing in IrMn maybe disposed on the IrMn layer. For the additional layer, for example, anfcc metal material in which the lattice spacing is nearly on the samelevel as in IrMn may be laminated over the IrMn layer. With thatconstitution, the thermal stability of the spin valve film could beimproved.

[0465] Where the MR-improving layer is provided below theantiferromagnetic layer as the underlayer for the antiferromagneticlayer, it will be effective for controlling the lattice spacing in theantiferromagnetic layer and, in addition, for enhancing the pinningability of the antiferromagnetic layer. Even to that case where theMR-improving layer is provided directly adjacent to theantiferromagnetic layer, not only ordinary pinned structures in whichthe pinned layer is directly contacted with the antiferromagnetic layerbut also Synthetic antiferromagnetic structures with Ru, Cr and otherssuch as those mentioned above are applicable. In the combinedconstitution with the antiferromagnetic layer, the antiferromagneticlayer and the MR-improving layer do not diffuse too much in thermaltreatment. Therefore, it is desirable that the material of theMR-improving layer does not form solid solution with that of theantiferromagnetic layer, or, when an γ-Mn-based antiferromagneticmaterial such as IrMn, RuRhMn or the like is used for theantiferromagnetic layer, the MR-improving layer is of an fcc metalmaterial or an hcp metal material so as to stably keep the crystalstructure of the antiferromagnetic layer.

[0466] Based on various advantages of specular reflection on theinterface of metal film/metal film and others mentioned above, themagnetoresistance effect device of the invention is intended to haveimproved MR characteristics, improved thermal stability and improvedmagnetization-pinning characteristics. For that device with specularreflection on the metal/metal interface therein, the following twopoints must be taken into consideration. First, since there is smallpotential difference in the metal/metal interface, the interface couldnot ensure large specular reflection if based on the conventional idea.Secondly, when the film thickness is increased to some degree in orderto ensure the specular reflection effect of the reflective film of ametal, the metal film will produce shunt current flows as having smallresistance, whereby the current to flow in the basic GMR unit willdecrease and the MR ratio in the device will be reduced.

[0467] It is believed that metal films are inferior to oxide films withrespect to their reflectivity. Though inferior to oxide films, metalfilms could still have good reflectivity. From the viewpoint ofindustrial applicability, metallic reflective films are superior toreflective films of oxides. Based on this point, the invention has beenherein completed.

[0468]FIG. 36 is a schematic view of a model of metal/metal interfacewith good specular reflection thereon. In place of ordinary electronpotential models generally employed in the art, herein used is anextremely simplified model for wave theory for facilitating theunderstanding of the invention. As in FIG. 36, when an electron having apredetermined Fermi wavelength has reached a metal/metal interface, thenthe wavelength of the electron shall change. In that condition, when theFermi wavelength of the electron is shorter in one metal film, thereflective film p, than the other metal film neighboring on the film p,then the electron as reached the film p at an angle θ smaller than thecritical angle θc (θc>θ) shall be all the time completely reflected onthe film p. With the difference between the Fermi wavelength of anelectron in the reflective film p and that in the neighboring metal filmbeing larger, the critical angle θc for the electron shall be larger,and, as a result, the mean reflectivity p as averaged for all electronsthat participate in electroconductivity shall be larger.

[0469]FIG. 37A and FIG. 37B are graphs indicating the ratio of the Fermiwavelength, Λ(p), in the reflective film p to the Fermi wavelength,Λ(GMR), in a GMR film neighboring on the reflective film p, Λ(GMR)/Λ(p), versus the critical angle θc. As is known from FIGS. 37A and 37B,the metal/metal interface could reflect electrons thereon to asatisfactory degree even though the electron wavelength difference isnot so significant. Needless-to-say, it is believed that the electronwavelength is infinite on a reflective film of an insulating material,and the critical angle θc for electrons on the reflective insulator filmis large. However, even for metal/metal interface, electrons couldreflect on the interface to a satisfactory degree. FIG. 38 is a graph ofthe data of the critical angle θc at which Au(Ag)/Cu interface producesspecular reflection, as calculated from the Fermi wavelength at theinterface. As is known from FIG. 38, the interface of Au(Ag)/Cu wellproduces satisfactory specular reflection thereon.

[0470] From the above, it is understood that, for the reflective filmwith metal/metal constitution, the important matters are that (1) theFermi wavelength of electrons in one metal film is as long as possibleand (2) the compositional steepness in the interface between the metalfilms is high. The Fermi wavelength is generally on the order of a fewangstrom. Therefore, if the compositional steepness is lost owing to theinterfacialdiffusionoverthatorder, thewavereflectionwill vary, dependingon the wavelength, whereby the electron transmission probability willincrease. Therefore, it is important how to increase the compositionalsteepness at the film interface and how to make the Fermi wavelengthvary to a great extent on that interface. However, regarding (1), therelationship between the Fermi wavelength and the specular reflection isnot as yet clarified, and the Fermi wavelength is difficult tocalculate. Therefore, it is not clear as to whether or not the condition(1) is indispensable herein. Therefore, we, the present inventors haveherein decided that the condition (2) is indispensable to the presentinvention.

[0471] For satisfying the condition (2), it is especially important thatthe different metals in the metal/metal film constitution do not formsolid solution when combined. If in the metal/metal system, metalprecipitation occurs easily on the interface through annealing, it willmuch increase the compositional steepness in the interface to furtherfacilitate specular reflection on the interface. Since the Fermiwavelength of electrons is naturally on the order of a few angstroms, itis desirable that the compositional steepness in the metal/metalinterface is dull on that order. Regarding the point (1) noted above, itis desirable that a metal film with a shorter electron wavelength isdisposed on the outer side of the magnetic layer while another metalfilm with a longer electron wavelength is on the outer side of theprevious metal layer, for enhancing the reflectivity of the metal/metalfilm constitution.

[0472] From the above, for really ensuring the specular reflection onthe metal/metal interface, it is understood that one practicable methodof material selection for the metal/metal film constitution is todispose an MR-improving layer of a metal not forming solid solution withthe element of the magnetic layer, on one side of the magnetic layerthat is opposite to the side of the spacer layer. In addition, it isdesirable to dispose the first metal film 4 a with a shorter electronwavelength, for example, on the outer side of the free layer 1 and todispose the second metal film 4 b with a longer electron wavelength onthe outer side of the film 4 a.

[0473] Where an alloy film is used as the reflective film, itsresistance is generally larger than that of pure metal films, if it doesnot form a completely regular alloy. In other words, the electronwavelength of the alloy film is long. This is advantageous forreflective films and is further advantageous in that the constituentelements of the alloy do not form solid solution with the elements ofthe neighboring film. The method of forming the alloy film of that typeis not limited to direct formation of the alloy film. Alternatively,plural films of alloying systems may be formed through lamination,whereupon an alloy may be formed in the interface of the laminate.However, when the free layer is thin, it is desirable that the specificresistance of the MR-improving layer adjacent to the free layer islower. (In this connection, when the free layer is thin, theMR-improving layer acts as the nonmagnetic high-conductivity layer inthe first embodiment.) Therefore, in that case, it is rather undesirableto form the alloy layer directly on the free layer.

[0474] For the reasons noted above, in the spin valve films 8 asillustrated in FIG. 32, FIG. 33 and FIG. 34, the MR-improving layer 4acting as the reflective film is so disposed that the metal film(concretely, the first metal film 4 a) not forming solid solution withthe magnetic layer (free layer 1) is adjacent to the magnetic layer(free layer 1); and the MR-improving layer 4 acting as the reflectivefilm is of a laminate film composed of a plurality of metal films 4 aand 4 b, or the MR-improving layer 4 is of the alloy layer 4 c. Thematerials for constituting the plural metal films 4 a and 4 b and thealloy layer 4 c are selected on the basis of the knowledge noted above.Where the MR-improving layer 4 is of a laminate film, it is desirablethat the first metal film having a shorter electron wavelength isdisposed adjacent to the magnetic layer 1 for specular reflection.However when the free layer thickness is thin enough to have spin-filtereffect, MR-improving layer 4 is preferred to have low resistivity. Theknowledge noted above shall apply to the other constitutive conditionsthan this.

[0475] The MR ratio in the MR film based on the specular reflection, orspin-filter effect when the free layer thickness is thin, noted above,is still kept as such even after annealing. This is because, owing tothe appropriate material selection for the MR-improving layer 4 (in thatthe specifically-selected material of the layer 4 does not form solidsolution with the elements in the neighboring layers), the compositionalsteepness in the interface in the film could be still maintained as sucheven after annealing. In other words, the MR characteristics ofconventional spin valve films are degraded in annealing owing to theinterfacial diffusion or mixing, but the spin valve films of theinvention can still maintain their as-deposited MR characteristics evenafter annealing. Accordingly, the spin valve films 8 of the inventionhave good thermal stability.

[0476] In the prior art spin valve film (e) mentioned above, the Cu/Aglaminate film is to enhance the specular reflection on its interface.This is because the surface roughness of the single-layered Cu film islarge, and the Ag film is laminated on the Cu film. The idea for theprior art film (e) is obviously different from that for the spin valvefilm of the invention in which the specular reflection on themetal/metal interface is intended to be augmented. Specifically, theprior art technique is for surface planarization, while the technique ofthe invention is for increasing the compositional profile in themetal/metal interface. Obviously, therefore, the material to belaminated differs between the prior art technique and the technique ofthe invention.

[0477] The MR-improving layer which is effective for improving thethermal stability of the MR device acts not only as themirror-reflective film but also acts for microcrystalline film structurecontrol, as so mentioned hereinabove, thereby contributing to theimprovement in the MR characteristics of the spin valve films 8. TheMR-improving layer is not limited to be below the free layer 1. Evenwhen disposed above the antiferromagnetic layer 6, as in FIG. 39 andFIG. 40 (MR-improving layer 4B), the layer well exhibits its functions.In those cases, the MR-improving layer 4B does not directly participatein magnetostriction control in the free layer. The MR-improving layer 4Bof a laminate film composed of a plurality of metal layers 4 a and 4 bor of an alloy layer 4 c (these 4 a, 4 b and 4 c are mentionedhereinabove) is disposed on the antiferromagnetic layer 6 of IrMn or thelike such as that mentioned above, and this acts for stabilizing thelattice spacing in the antiferromagnetic layer. As a result, dislocationon the interface of magnetic layer 2/antiferromagnetic layer 6 isprevented, whereby the thermal stability of the spin valve films 8 ismuch more improved.

[0478] When the lattice spacing in the antiferromagnetic layer issuitably controlled by the MR-improving layer, the other magnetizationpinning characteristics of the films 8 are also improved. Moreeffectively for the lattice spacing control, the MR-improving layer actsas the underlayer for the antiferromagnetic layer. This is especiallyeffective in bottom type spin valve films or dual spin valve films. Evenin the films of those types, the lattice spacing in theantiferromagnetic layer could be freely and appropriately controlled bythe laminated fcc metal or hcp metal film or alloy film specificallyincorporated therein, whereby the magnetization pinning characteristicsof the films could be improved (with respect to the magnetic couplingbias field and the thermal stability).

[0479] Where the MR-improving layer 4B of a laminate film composed of aplurality of metal films 4 a and 4 b is disposed on theantiferromagnetic layer 6, it is desirable that the second metal film 4b of a metal having small surface energy, such as Au or the like, isdisposed to be adjacent to the antiferromagnetic layer 6. This isbecause, if the second metal film 4 b of Au, Ag or the like is adjacentto the protective film 7 of Ta or the like, the constituent metal of Au,Ag or the like will diffuse into the protective film 7 to lower thethermal stability. Therefore, it is desirable that the first metal film4 a of Cu or the like is disposed adjacent to the protective film 7. TheMR-improving layer 4B above the antiferromagnetic layer 6 may be of alaminate film of first metal film 4 a/second metal film 4 b/first metalfilm 4 a.

[0480] As mentioned hereinabove, the MR-improving layer 4 a of ametallic laminate film or an alloy layer is effective for reducing themagnetostriction in the free layer 1 of a Co-based magnetic materialsuch as Co, a CoFe alloy or the like. If the single-layered magneticlayer 1 of CoFe is subbed with only a underlayer of simple Cu, negativemagnetostriction in the layer 1 will be great over −1 ppm, since thelattice spacing in the layer 1 is too small. On the other hand, if thesingle-layered magnetic layer 1 of CoFe is subbed with only a underlayerof simple Au, positive magnetostriction in he layer 1 will be great over+1 ppm, since the lattice spacing in the layer 1 is too large.

[0481] As opposed to those, when the MR-improving layer 4 of a metalliclaminate film or alloy layer 4 c that comprises at least one elementselected from Cu, Au, Ag, Pt, Rh, Pd, Al, Ti, Zr, Hf and Ir is providedas the underlayer for the free layer 1 of a Co-based magnetic materialsuch as Co, a CoFe alloy or the like, the fcc(111) orientation in thelayer 1 can be improved, and, in addition, the lattice spacing in thelayer 1 can be controlled to fall within a range effective formagnetostriction reduction. For example, the d(111) lattice spacing inthe layer 1 can be controlled to fall between 0.2055 and 0.2085nanometers. It is desirable that, in the MR-improving layer 4 which actsas the underlayer below the free layer 1, fcc-d(111) is larger than0.2058 nanometers. The d-(111) lattice spacing control in the layer 4maybe effected, for example, as follows: When the layer 4 is of alaminate film of Au—Cu, the ratio of the Au thickness to the Cuthickness is varied for the intended control. When the layer 4 is of analloy film of Au—Cu, the alloying compositional ratio of Au to Cu isvaried for the intended control.

[0482] Concretely, it is desirable that the composition of the Au—Cualloy for the layer 4 falls within a range of Au₂₅Cu₇₅ to Au₇₅Cu₂₅ (at.%). Where the layer 4 is of a laminate film of alloy layers and metalfilms, it is desirable that it has an Au-richer composition in somedegree, as compared with the layer 4 of a single-layered Au—Cu alloyfilm. For example, the laminate film of the layer 4 may have acomposition of Au₂₅Cu₇₅ to Au₉₅Cu₅ (at. %).

[0483] In the spin valve films 8 of FIG. 32, FIG. 33 and FIG. 34, thefree layer 1 is positioned in the lower site. However, these are notimitative. The invention encompasses bottom type spin valve films 8 ordual element-type spin valve films 8 in which the free layer 1 ispositioned in the upper site, for example, as in FIG. 41 and FIG. 42. Inparticular, inthose bottom type spin valve films and dual spin valvefilms, the effect of the MR-improving layer as the subbing film for theantiferromagnetic layer is significant.

[0484] The spin valve films 8 of FIG. 41 and FIG. 42 has a structure ofnonmagnetic underlayer 5/MR-improving layer 4/antiferromagnetic layer6/pinned magnetic layer 2/nonmagnetic spacer layer 3/free layer1/MR-improving layer 4/protective layer 7 as laminated in that order onthe substrate 9. In the embodiment of FIG. 41, the MR-improving layer isof an alloy layer 4 c. In the embodiment of FIG. 42, the MR-improvinglayer 4 is of a laminate film of a plurality of metal films 4 a and 4 b.As in FIG. 34, a laminate film of a metal film 4 a and an alloy layer 4c is also employable for the layer 4 in those embodiments.

[0485] Where the MR-improving layer 4 as disposed above the freelayerlis of alaminate film, as inFIG. 42, it is desirable that the first metallayer 4 a of Cu or the like is disposed adjacent to the protective layer7, like in the upper MR-improving layer 4 in FIG. 39. Therefore, in FIG.42, the MR-improving layer 4 above the free layer 1 is of a laminatefilm of first metal film 4 a/second metal film 4 b/first metal film 4 a.

[0486] In the bottom type spin valve films, the MR-improving layer whichis the underlayer for the antiferromagnetic layer acts for film growthcontrol, thereby improving the thermal stability and the pinningcharacteristics of the films through lattice spacing control andmicrostructure control, and those effects of the MR-improving layerdiffer from the effects of the free layer for magnetostriction controland for specular reflection improvement. Therefore, so far as they areproduced under the condition under which the microstructure of theantiferromagnetic layer therein is kept good, the bottom type spin valvefilms of the invention could fully exhibit their good capabilities onlywith the MR-improving layer being disposed adjacent to the free layereven in the absence of the MR-improving layer below theantiferromagnetic film or even when the antiferromagnetic layer isdisposed above an ordinary buffer layer of Ta, Ti or the like as in theordinary subbing constitution in conventional reverse structures.

[0487] In the bottom type spin valve films 8, where the MR-improvinglayer 4 as above is disposed adjacent to the free layer 1, thecompositional steepness in the interface between the free layer 1 andthe MR-improving layer 4 is kept to give specular reflection thereon,whereby the MR characteristics of the films could be ensured. When thefree layer thickness is thin and the compositional steepness in theinterface between the free layer and the MR-improving layer 4 is kept togive the spin-filter effect, whereby the MR characteristics of the filmscould be ensured. In those, as so mentioned hereinabove, the MR ratiosupported by the specular reflection or by the spin-filter effect isstill kept even after annealing, and the films could have good thermalstability.

[0488] In the reverse structure-type spin valve films 8 mentioned above,at the interface of free layer 1/MR-improving layer 4, and even at theinterface of first metal film 4 a/second metal film 4 b at the interfaceof second metal film 4 b/third metal film 4 a in the MR-improving layer4 (FIG. 42) reflect electrons. Therefore, the constitution of the films8 differs from that of the prior art film (e) noted above having a Cu/Aulaminate film in that the surface of the Ag film reflects electrons inthe latter. In addition, the present invention has solved the problemwith the prior art film (d) which loses the reflectivity when Ta islaminated on the surface of the Au film therein. This is because thepresent invention utilizes thespecularreflectiononthemetal/metalinterface, which being characterized in that each filmthickness is specifically defined in consideration of the Fermiwavelength of electrons and that the components in the interface do notform solid solution.

[0489] In the prior art constitution (d), Ta is laminated on anextremely thin Au layer, of which the thickness is only 0.4 nanometersand is nearly the same as the Fermi wavelength, and Ta will form solidsolution with Au. In this, therefore, it is obvious that, even when theCo-Au interface could be reflective, its reflection is lost as a whole.If the thickness of the Au film therein is made larger than the Fermiwavelength, such a thick Au film could be reflective as being influencedlittle by the interfacial diffusion of Ta thereinto, but, on the otherhand, negative influences of shunt current flow on the Au film will beenlarged. In place of the Au/Ta interface as in the prior artconstitution, if a laminate film of Au/Cu/Ta in which the Cu layer doesnot form solid solution with Ta is used, the Au interface is notdisturbed in the laminate. In addition, if an ultra-thin Cu layer isinserted, for example, between the interface of CoFe and Au, long-termdiffusion of Au into the nonmagnetic spacer layer could be prevented,and, in addition, the reflectivity of the resulting laminate could beenhanced since the Cu layer having a short Fermi wavelength isinterposed between CoFe and Au.

[0490] In the embodiments mentioned above, the MR-improving layer isdisposed adjacent to the free layer 1 or the antiferromagnetic layer 6.Different from those, other embodiments where the MR-improving layer 4is disposed inside the free layer 1 or inside the pinned magnetic layer2, for example, as in FIG. 43, could produce the same results as above.

[0491] In the spin valve film 8 of FIG. 43, the free layer 1 is composedof, for example, an NiFe layer 1 a and a CoFe layer 1 b, and theMR-improving layer 4 of a laminate film of a plurality of metal films 4a and 4 b is interposed between the layers 1 a and 1 b. In this, theNiFe layer 1 a and the CoFe layer 1 b are ferromagnetically coupled toeach other via the MR-improving layer 4 existing therebetween, and thoseplural layers are integrated and magnetically acts as the integratedfree layer 1. Where the MR-improving layer 4 is interposed in theinterface of NiFe layer 1 a/CoFe layer 1 b (in this case, the layer 4does not form solid solution with both the layers 1 a and 1 b in theinterface), the NiFe layer 1 a and the CoFe layer 1 b must be integratedto act as the integrated free layer 1. In this case, therefore, theMR-improving layer 4 to be interposed must be thin. The MR-improvinglayer may also be interposed in the pinned magnetic layer 2. In thiscase, two or more magnetic films constituting the pinned magnetic layer2 are ferromagnetically or antiferromagnetically coupled to each other.The mode of ferromagnetic or antiferromagnetic coupling in the layer 2shall be determined, depending on the material and the thickness of theMR-improving layer 4 to be interposed in the layer 2.

[0492] The magnetoresistance effect device of the embodiments mentionedhereinabove may be mounted on separated recording/reproducing magneticheads, as the reproduction device part, for example, as in FIG. 44 andFIG. 45. Not limited to magnetic heads, the magnetoresistance effectdevice of the invention is also applicable to other various magneticmemory systems such as magnetoresistance effect memories (MRAM), etc.

[0493]FIG. 44 and FIG. 45 show the structures of embodiments of aseparated recording/reproducing magnetic head which incorporates themagnetoresistance effect device of the invention as the reproductiondevice part. These are sectional views of separatedrecording/reproducing magnetic heads as seen in the medium facingdirection.

[0494] In those drawings, 21 is a substrate with a layer of Al₂O₃, suchas Al₂O₃.TiC. On the main surface of the substrate 21, formed is a lowermagnetic shield layer 22 of a soft magnetic material which includes NiFealloys, FeSiAl alloys, amorphous CoZrNb alloys, etc. On the lowermagnetic shield layer 22, formed is a spin valve GMR film 24 via a lowerreproduction magnetic gap 23 of a nonmagnetic insulating material suchas A₂lO₃ or the like. As the spin valve GMR film 24, used is the spinvalve film 8 of any of the embodiments mentioned hereinabove.

[0495] In FIG. 44, the spin valve GMR film 24 is so etched that itsprofile could have a desired track width. The etching is to remove theouter region of the film 24 that oversteps the recording track width. Atthe both outer edges of the spin valve GMR film 24, disposed are films25 which are to apply bias magnetic field to the film 24. The pair ofbias magnetic field applying films 25 are in abutted junction to theedges of the spin valve GMR film 24.

[0496] On the pair of bias magnetic field applying films 25, formed area pair of electrodes 26 of Cu, Au, Zr, Ta or the like. To the spin valveGMR film 24, supplied is sense current from the pair of electrodes 26.These spin valve GMR film 24, paired bias magnetic field applying films25 and paired electrodes 26 constitute a GMR reproduction device part27. As mentioned above, the GMR reproduction device part 27 has aso-called abutted junction structure.

[0497] In FIG. 45, the pair of bias magnetic field applying films 25which are to apply a bias magnetic field to the spin valve GMR film 24are previously formed between the spin valve GMR film 24 and the lowerreproduction magnetic gap 23 in the region not for the trackwidth. Thepair of bias magnetic field applying films 25 are separated by apredetermined space therebetween, and the layers of the part outside thereproduction track for the spin valve GMR film 24 are laminatedthereover. On the spin valve GMR film 24, the bias magnetic fieldapplying films 25 maybe laminated only at its both edges, if desired.

[0498] On the spin valve GMR film 24, formed are the pair of electrodes26. The substantial reproduction track width of the spin valve GMR film24 is defined by the distance between the pair of electrodes 26. Thesespin valve GMR film 24, paired bias magnetic field applying films andpaired electrodes 26 constitute the GMR reproduction device part 27having an overlaid structure.

[0499] In FIG. 44 and FIG. 45, an upper reproduction magnetic gap 28 ofa nonmagnetic insulating material, which may be the same as that of thelower reproduction magnetic gap 23, is formed on the GMR reproductiondevice part 27. On the upper reproduction magnetic gap 28, formed is anupper magnetic shield layer 29 of a soft magnetic material which may bethe same as that of the magnetic shield layer 22. These constituentelements form a reproducing head, shield-type GMR head 30.

[0500] A recording head, thin-film magnetic head 31 is formed on theshield-type GMR head 30. The lower recording magnetic pole of thethin-film magnetic head 31 and the upper magnetic shield layer 29 formone and the same magnetic layer. In other words, the upper magneticshield layer 29 of the shield-type GMR head 30 acts also as the lowerrecording magnetic pole of the thin-film magnetic head 31. On the lowerrecording magnetic pole 29 acting also as the upper magnetic shieldlayer, formed are a recording magnetic pole gap 32 of a nonmagneticinsulating material such as Al₂O₃ or the like, and an upper recordingmagnetic pole 33 in that order. Behind the medium-facing site, formed isa recording coil (not shown) which is to apply a recording magneticfield to the lower recording magnetic pole 29 and to the upper recordingmagnetic pole 33.

[0501] The reproducing head, shield-type GMR head 30, and the recordinghead, thin-film magnetic head 31 constitute the separatedrecording/reproducing magnetic head. The separated recording/reproducingmagnetic head of that type is combined with a head slider, and mountedon a magnetic head assembly, for example, as in FIG. 46. The magnetichead assembly 60 of FIG. 46 is provided with, for example, an actuatorarm 61 having a bobbin part for holding a driving coil, and a suspension62 is connected to one end of the actuator arm 61.

[0502] To the tip of the suspension 62, fitted is a head slider 63 whichis provided with the separated recording/reproducing magnetic head ofthe embodiment mentioned above. The suspension 62 is provided with alead 64 which is for writing and reading signals, and the lead 64 iselectrically connected to each electrode in the separatedrecording/reproducing magnetic head as incorporated in the head slider63. In the drawing, 65 are electrode pads in the magnetic head assembly60.

[0503] The magnetic head assembly 60 of the illustrated type is mountedon a magnetic recording/reproducing system such as a magnetic discsystem or the like, for example, as in FIG. 47. FIG. 47 shows theoutline structure of a magnetic disc system 50 incorporating a rotaryactuator.

[0504] As illustrated, the magnetic disc 51 is fitted to a spindle 52,and is rotated by a motor (not shown) that responds to the controlsignal from a driving system control source (not shown). The magnetichead assembly 60 is so mounted on the system 50 that the head slider 63as fitted to the tip of the suspension 62 could float above the magneticdisc 51 for the intended information recording and reproduction. Whilethe magnetic disc 51 is rotated, the medium-facing site (ABS) of thehead slider 63 is held above the magnetic disc 51 via a predeterminedfloating distance (from 0 to 100 nanometers).

[0505] The actuator arm 61 of the magnetic head assembly 60 is connectedto a voice coil motor 51 which is one type of a linear motor. The voicecoil motor 53 comprises a driving coil (this is coiled in the bobbinpart of the actuator arm 61 and is not shown herein) and a magneticcircuit. The magnetic circuit comprises facing permanent magnets andfacing yolks all disposed to sandwich the driving coil therebetween. Theactuator arm 61 is held by ball bearings (not shown) as disposed in twosites, upper and lower sites of the fixed shaft 54, and is rotatable andslidable by the power of the voice coil motor 53.

[0506] The above is to exemplify one embodiment of the invention forseparated recording/reproducing magnetic heads. Not limited to only suchheads, the magnetoresistance effect device of the invention isapplicable to any other head structures, for example, to an integratedrecording/reproducing magnetic head that comprise one and the samemagnetic yolk for both the recording head and the reproducing head.Still not limited to only magnetic heads, the magnetoresistance effectdevice of the invention is further applicable to any other magneticmemory systems such as magnetoresistance effect memories (MRAM), etc.

[0507] The invention is described in more detail with reference to thefollowing Examples, in which the samples produced were tested andanalyzed for their characteristics.

EXAMPLE a

[0508] In Example a, produced was a spin valve film of 5 nanometer Ta/1nm Au/1 nm Cu/4 nm CoFe/2.5 nm Cu/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta,in a DC magnetron sputter. The vacuum degree in the sputter was at most1×10⁻⁷ Torr, in which the argon pressure was from 2 to 10 mTorr. Infabricating magnetic heads, the film is formed on the Al₂O₃ gap on anAlTiC substrate. It has been confirmed that the properties of the filmdo not vary.

[0509] The spin valve film had an MR ratio of 9.6% in the as-depositedcondition, but after having been annealed at 250° C. for 4 hours in amagnetic field of 5 kOe, its MR ratio was still 9.0%. Themagnetostriction in the film was on the order of at most ±10⁻⁶. Hk of afilm sample having been annealed in a magnetic field applied in thedirection of the easy axis is defined as saturation Hk of the filmsample. Hk of the film produced herein was about 8 Oe and was small.This support the soft magnetic characteristics of the film. Hc of thefilm in the easy axis direction fell between 0 and 3 Oe, and was small.

[0510] In the film, the laminate film of Au/Cu is the MR-improvinglayer. In the interface between Au and Cu, formed is their alloy. In theinterface between Cu and CoFe, formed is no solid solution. In theinterface between Ta and Au, formed is their solid solution. However,since the thickness of the laminate of Au/Cu is much longer than theelectron wavelength, the electron reflection on the interface issatisfactory. Therefore, the solid solution interface existing in thefilm causes no problem for electron reflection. In the presence of thefcc-structured Au/Cu underlayer, the layer of CoFe was well oriented infcc(111) orientation. In addition, the d(111) spacing in CoFe is 0.2074nanometers, and the magnetostriction therein was controlled to be small.

[0511] The cross section of the spin valve film of this Example 1 wasobserved through TEM (transmission electron microscopy). As a result, itwas confirmed that the GMR basic unit moiety of CoFe/Cu/CoFe was formedon the underlayer of Au/Cu in regular layer by layer, and was orientedin fcc (111) orientation. In microdiffraction of the free layer, CoFelayer part, the fcc-d(111) spacing was found 0.2074 nanometers. Thespacing is favorable to magnetostriction control. FIG. 48 shows the XRDpattern of the spin valve film. Through the X-ray diffraction of thefilm, the fcc-d(111) spacing in CoFe was found 0.2074 nanometers.

[0512] In the XRD profile in FIG. 48, the peaks 1, 2 and 3 are for IrMn,and the peak 4 will be the fcc(111) peak for the laminate film ofCoFe/Cu/CoFe. The d-spacing in the free layer only is difficult todetermine. In this case, the d-spacing for the peak 4 is considered asthe d-spacing in the free layer.

[0513] In place of the underlayer of 1 nm Au/1 nm Cu, when a underlayerof 2 nm Cu onlywas used, then the fcc-d(111) spacing in CoFe decreasedto 0.2054 nanometers and the magnetostriction increased in the negativeside. On the other hand, when a underlayer of 2 nmAu only was used, thenthe fcc-d(111) spacing in CoFe increased to 0.2086 nanometers and themagnetostriction increased in the positive side. Only when theunderlayer of Au/Cu was used, the suitable spacing of 0.2074 nanometerswas realized.

[0514] The thermal stability of the prior art film (g) where theunderlayer is of Cu is not good. However, the thermal stability of thefilm of this Example where the underlayer is of a laminate film of Au/Cuis good. One reason will be because of the difference in the latticespacing between the two which will have some influence on themagnetostriction of the films. Precisely, the lattice spacing isnarrowed on the Cu underlayer, whereby the lattice unconformity in theinterface to IrMn is augmented and the distortion is enlarged. When thefilm with such large distortion is annealed, the distortion is relaxedwhereby the interface between the pinned magnetic layer and theantiferromagnetic film becomes diffusive. This influence is larger whenthe IrMn layer is thicker. On the other hand, the lattice spacing in theunderlayer of Au/Cu is nearer to that in IrMn. Therefore, the film ofCoFe/Cu/CoFe to be laminated on the Au/Cu layer is, contrary to the casehaving the simple Cu underlayer, to have a distorted lattice of whichthe lattice constant is near to that of IrMn. As a result, the influenceof annealing on the distortion relaxation in the case having thelaminate underlayer of Au/Cu will be smaller.

[0515] In the other prior art constitution (h) having an Au underlayer,the lattice spacing is larger, contrary to that in (g). In the case (h),therefore, the distortion energy of CoFe/Cu/CoFe is too large so thatthe interfacial dislocation occurs with ease. As a result, the film (h)is degraded in initial annealing. When the Au layer is directlylaminated on the CoFe layer, Au will diffuse even into the nonmagneticspacer layer of Cu while passing through the intergranular boundaries.If Au reaches the nonmagnetic spacer layer, the MR ratio in the filmimmediately decreases. The MR ratio reduction worsens the long-termthermal stability of the film. However, if the laminate film of Au/Cu isdisposed as the underlayer below CoFe, the Cu layer acts as a stopper toprevent Au diffusion, and the long-term thermal stability of the film isthereby stabilized.

[0516] The underlayer of Ta is a buffer layer necessary fortwo-dimensional growth of Au. If Au is directly formed on amorphousAl₂O₃, it will island-wise grow. In that condition, where the pinnedmagnetic layer and the free layer are magnetically coupled to each othervia the spacer layer, Hin will increase. In producing practical devices,the films are formed on processed substrates. For the devices,therefore, the buffer layer is indispensable for stable film formation.In this Example, Ta was used for the underlayer. Apart from this, anyothers of Ti, Zr, Cr, W, Hf, Nb, their alloys, and their oxides andnitrides are usable for the underlayer.

[0517] In the prior art film (f), the underlayer below Au has a totalthickness of 220 nanometers. As opposed to this, in this Example, the Taunderlayer is enough to prevent island-like growth of Au and toplanarize the Au surface. The interface between Au and the overlyingCu/CoFe film is also planarized. In addition, the film of this Exampledoes not require high-temperature thermal treatment at 350° C. The bestthermal treatment to which the film of this Example is subjected is at270° C. and for 4 hours or so. In that thermal treatment, thecompositional steepness in the interlayer is kept best. For thesereasons, the nonmagnetic underlayer of Ta is important. When combinedwith any other ordinary underlayer, the Ta underlayer planarizes the Aufilm formed thereon.

[0518] When any of 5 nanometer Ti, 5 nm Zr, 5 nm W, 5 nm Cr, 5 nm V, 5nm Nb, 5 nm Mo, 5 nm Hf and their alloys (5 nanometer Thick) was used asthe nonmagnetic underlayer, thesame results as above were also obtained.When any of 0.5 to 2 nm Au/0.5 to 2 nm Cu, 0.3 to 1 nm Au/0.3 to 1 nmCu/0.3 to 1 nm Au/0.3 to 1 nm Cu, or 0.5 to 5 nm AuCu/0.5 to 2 nm Cu wasused as the MR-improving layer, the same results as above were alsoobtained.

[0519] The MR-improving layer may be of a two-layered or even moremulti-layered film, or a single-layered alloy film. However, when itdoes not contain an additive element capable of increasing resistanceand if its thickness is large, the shunt current flow will increase.Therefore, the thickness of the MR-improving layer is preferably at most5 nanometers. However, it must have an additional seed effect for fccorientation as the underlayer, it is desirable that the MR-improvinglayer to be disposed below the magnetic layer has a thickness of from 2to 5 nanometers or so.

[0520] Except the combination of Au-Cu, other examples of the laminatefilm and the alloy layer that may be combined with the magnetic layer ofa Co-based alloy include Ru—Cu, Au—Cu, Pt—Cu, Rh—Cu, Pd—Cu, Ir—Cu,Ag—Pt, Ag—Pd, Ag—Au, Au—Pt, Au—Pd, Au—Al, etc. In those combinations,the essential element in the MR-improving layer to be disposed adjacentto the Co-based magnetic layer is any of Cu, Au and Ag.

[0521] Regarding the film constitution, any of two-layered laminates,such as Au—Cu, Ru—Cu illustrated herein, or three-layered or moremulti-layered laminates, or even single-layered or multi-layered alloyfilms are employable. Regarding the film thickness, the same as that forthe film of Au—Cu illustrated herein shall apply to those modifications.When the films do not contain a third element, their thickness ispreferably from 2 to 3 nanometers or so in terms of the total thickness.

[0522] Preferred combinations to be applied to the Co-based magneticlayer are Au—Cu, Ag—Pt, Au—Pd, Au—Ag, Pt—Cu and the like, as they ensuremicrostructure films and as they form solid solution with ease. Of thosecombinations, the best one ensuring good lattice constant control isdetermined.

[0523] Like in the case where the magnetic layer is of a Co-basedmaterial, the combinations for the laminate films or alloy layers forthe MR-improving layer to be disposed adjacent to the magnetic layer ofanNi-basedmaterial include Au—Pt, Au—Pd, Au—Ag, Au—Al, Ag—Pt, Ag—Pd,Ru—Rh, Ru—Ir, Ru—Pt, etc. In those combinations, the essential elementin the MR-improving layer to be disposed adjacent to the Ni-basedmagnetic layer is any of Au, Ag and Ru. Regarding the film constitutionand the film thickness, the same as that for the Co-based magnetic layercould apply also to the case of the Ni-based magnetic layer.

[0524] The two elements constituting the MR-improving layer may be thosenot forming solid solution. For example, in the case of Co-basedmagnetic layer, the MR-improving layer may be of a laminate film ofCu-Ru or Cu-Ag. Those combinations not forming solid solution are notsuitable for alloy layers. This is because alloy layers of thosecombinations will readily give separated two phases. Therefore, thosecombinations are preferably used for laminate films. Specific examplesof the Ni-based magnetic layer include NiFe, NiFeCr, NiFeNb, NiFeRh,etc.

[0525] Regarding the pinned magnetic layer constitution, the pinnedmagnetic layer is directly laminated on the antiferromagnetic layer inthe case illustrated herein. In place of the simple structure, alsoemployable are Synthetic antiferromagnetic structures. For example, inplace of 2.5 nm CoFe/7 nm IrMn, employable are 3 nm CoFe/0.9 nm Ru/3 nmCoFe/7 nm IrMn, 3 nm CoFe/0.9 nm Cr/3 nm CoFe/7 nm IrMn, etc. Thethickness of two pinned layer may be different each other.

[0526] The antiferromagnetic film may be of any material of PtMn, NiMn,RuRhMn, CrMn, FeMn, NiO, etc. The material of the pinned magnetic layermay be any of Co or NiFe.

[0527] The nonmagnetic underlayer is not limited to only metal films ofTa, etc. For example, oxide films of TaO_(x) or the like are alsoemployable. Using the underlayer of TaO_(x) in place of Ta gave the samegood results. In this case, electrons not reflected on the MR-improvinglayer could be reflected on the interface of TaO_(x)underlayer/MR-improving layer in which the potential difference islarge, whereby theMR ratio in the film was much more increased. However,if CoFe is formed directly on the underlayer of TaO_(x), it could not beoriented in fcc(111) orientation or could not have a satisfactoryfcc-d(111) spacing favorable to magnetostriction control. As opposed tothe case, a underlayer of TaO_(x)/Au/Cu is good in practicalapplications. In place of TaO_(x), also employable are other oxides ofTi, Zr, Cr, W, Hf, Nb, etc. Further employable are nitrides such as TiN,TaN.

EXAMPLE b

[0528] In this Example b, produced was a spin valve film of 5 nanometerTa/1 nm Au/1 nm Cu/4 nm CoFe/2.5 nm Cu/2.5 nm CoFe/7 nm IrMn/0.5 nmAu/0.5 nm Cu/5 nanometer Ta, in the same manner as in Example a.

[0529] The lattice constant of the Au/Cu laminate film, which is theupper MR-improving layer, is nearer to that of IrMn, than that of thelaminate film of CoFe/Cu/CoFe. Therefore, forming the laminate of Au/Cuon IrMn stabilizes more the lattice constant of IrMn, whereby thethermal stability of the film is much more improved. Disposing the Aulayer directly below the protective film of Ta gives a structure wherethe Au layer having small surface energy is directly below the Ta layerhaving large surface energy. In that structure, Au readily diffuses intoTa to degrade the thermal stability of the film. Therefore, disposing Auor Ag directly below Ta is unfavorable. Like in this Example, it isdesirable that the Ta protective film is formed via the Cu layer. Analloy layer of AuCu gives the same good results.

EXAMPLE c

[0530] In this Example c, produced was a spin valve film of 5 nanometerTa/5 nm NiFeCr/1 nm Au/1 nm Cu/3 nm CoFe/2.5 nm Cu/2.5 nm CoFe/7 nmIrMn/5 nanometer Ta, in the same manner as in Example 1. In this spinvalve film, the free layer is of a laminate film of 5 nm NiCoFe and 3 nmCoFe as separated by Au/Cu existing therebetween.

[0531] As one comparative case to this Example, prepared was a spinvalve film of 5 nanometer Ta/5 nm NiFeCr)/3 nm CoFe/2.5 nm Cu/2.5 nmCoFe/7 nm IrMn/5 nanometer Ta also in the same manner as above.

[0532] The comparative spin valve film had an MR ratio of 8.6% in theas-deposited condition, but after having been annealed at 250° C. for 4hours, its MR ratio lowered to 6.6%. The MR ratio reduction was 23%.This is because CoFe and NiFeCr form solid solution in this structure.In the as-deposited comparative film, the constituent elements are notmixed so much in the CoFe/NiFeCr interface and the film had a high MRratio. However, after annealed at 250° C. for 4 hours, the CoFe/NiFeCrinterface was readily disturbed. In this comparative case, added wasabout 4% of Cr to NiFe for current shunting in NiFeCr. The same resultswere also obtained in the case having Ni₈₁Fel₉ (at. %).

[0533] As opposed to the comparative case, interposing the Au/Culaminate film between CoFe and NiFeCr as in the case of this Example 3prevents the element diffusion in the interface therebetween. As aresult, the as-deposited film of Example 3 had an MR ratio of 8.7%, andeven after annealed at 250° C. for 4 hours, the annealed film still hadan MR ratio of 8.1%. This, in this film, the MR ratio reduction afterannealing is well retarded. One reason for this is that, owing to thediffusion preventing effect of the interposed Au/Cu layer, theinterfacial reflection on the CoFe layer was still kept good even afterannealing.

[0534] In place of 1 nm Au/1 nm Cu, also employable is any of 0.5nmAu/0.5 nmCu, 0.5 nmCu/0.5 nmAu, 0.3 nmAu/0.3 nmCu/0.3 nm Au, 0.3 nmAu/0.3 nm Cu/0.3 nm Au/0.3 nm Cu, 0.5 nm AuCu/0.5 nm Cu, 1 nm AuCu/0.5nm Cu, 0.5 nm Ag/0.5 nm Cu, 0.5 nm Cu/0.5 nm Ag, 0.3 nm Ag/0.3 nm Cu/0.3nm Ag, 0.3 nm Ag/0.3 nm Cu/0.3 nm Ag/0.3 nm Cu, 0.3 nm Pt/0.3 nm Cu, 0.5nm Cu/0.5 rim Pt, 0.5 nm Pt/0.5 nm Cu, 0.5 nm Pt, 0.5 nm Pt/0.5 nmCu/0.5 nm Pt/0.5 nm Cu, 0.5 to 1.5 nm AuCu, etc. Those gave the samegood results as herein.

[0535] The reason why NiFeCr was used as the second magnetic layerherein is as follows: Adding Cr to NiFe increases resistivity ρ, withoutdrastic reducing Ms, whereby the shunt current is reduced. In order toprevent the increase in the magnetostriction, λ, in the positive site,which is caused by the Cr addition, it is desirable that the ratio of Nito Fe is shifted to the Ni-rich site in some degree from the ordinaryzero-magnetostriction composition of Ni:Fe=81:19. One preferredcomposition is Ni₈₁Fe₁₅Cr₄, which satisfactorily controls all Ms, ρ andmagnetostriction. Apart from this, also employable are Ni₈₀Fe₂₀, NiFeNb,NiFeRh, etc.

EXAMPLE d

[0536] In this Example d, produced was a spin valve film of 5 nanometerTa/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/2.5 nm Cu/4 nm CoFe/0.5 nmCu/0.5 nm Au/0.5 n Cu/5 nanometer Ta, in the same manner as in Examplea.

[0537] The film produced herein is a so-called bottom type spin valvefilm in which the pinned magnetic layer is below the nonmagnetic spacerlayer. The upper Cu/Au/Cu layer is the MR-improving layer, by which thethermal stability of the film and also the MR ratio in the film areincreased. The lower Au/Cu layer is the subbing film for IrMn, whileadditionally acting as the MR-improving layer for stabilizing thelattice constant of IrMn. The as-deposited film had an MR ratio of 10%,and after annealed at 250° C. for 4 hours, the annealed film had an MRratio of 9.5%. The Cu/Au interface formed an alloy of AuCu.

[0538] The upper Ta in the film of this Example d is the protectivefilm, and this is not intended to be reflective. In this Example d, theCu/Au/Cu layer is the MR-improving layer. Therefore, in this, theCoFe/Au interface and the Cu/Au interface (or the AuCu alloy layer)shall be reflective. Thus, the constitution of the film of this Exampleobviously differs from the prior art constitution of (e) or (d)mentioned above. In addition, in this, the ultra-thin Cu layer isinterposed in the CoFe/Au interface, by which long-term diffusion of Auinto the nonmagnetic spacer layer of Cu is prevented. Moreover, in this,since the Au layer is disposed via the layer having a short Fermiwavelength, the interlayer reflection is much augmented.

[0539] In place of the MR-improving layer of 1 nm Au/1 nm Cu, alsoemployable is any of 0.5 to 3 nm Au/0.5 to 3 nm Cu, 0.5 to 3 nm Cu/0.5to 3 nm Au/0.5 nm Cu, 0.5 to 3 nm AuCu/0.5 to 3 nm Cu, 0.5 to 3 nmCu/0.5 to 3 nm AuCu/0.5 to 3 nm Cu, 0.5 to 3 nm Ag/0.5 to 3 nm Cu, 0.5to 3 nm Cu/0.5 to 3 nm Ag/0.5 to 3 nm Cu, 0.5 to 3 nm Pt/0.5 to 3 nm Cu,0.5 to 3 nm Cu/0.5 to 3 nm Pt/0.5 to 3 nm Cu, 0.5 to 3 nm PtCu/0.5 to 3nm Cu, 0.5 to 3 nm Cu/ 0.5 to 3 nm PtCu/0.5 to 3 nm Cu, etc. All thoselayers gave the same good results as herein.

[0540] Regarding the materials for the other layers, the same as inExample a may be referred to. The MR-improving layer as laminated abovethe free layer in this Example d is not needed to act additionally as aseed layer. Therefore, in this, the thickness of this MR-improving layermay be thin to have a thickness of 1 nanometer or so. However, if thelayer is too thick, it will unfavorably increase shunt current, as inExample a. Therefore, the thickness of this layer is preferably at most5 nanometers.

[0541] The MR-improving layer below the antiferromagnetic layer is tocontrol the lattice spacing in the antiferromagnetic layer, therebypreventing the interfacial mixing in the interface between the pinnedmagnetic layer of CoFe and the antiferromagnetic layer (the interfacialmixing will be caused by lattice misfit between the two layers). Inaddition, while controlling the lattice spacing in the antiferromagneticlayer, the MR-improving layer is to improve the pinning characteristicsof the pinned magnetic layer. Concretely, the MR-improving layer may beany of laminate films or alloy films of Al—Cu, Pt—Cu, Rh—Cu, Pd—Cu,Ir—Cu, Ag—Pt, Ag—Pd, Ag—Au, Au—Pt, Au—Pd, Au—Al, Ru—Rh, Ru—Ir, Ru—Pt,Ru—Cu, or Ag—Au.

[0542] As the MR-improving layer suitable to each antiferromagneticlayer, laminate films or alloy films of two elements selected from Cu,Au, Ag, Pt, Rh, Ru, Pd, Al, Ti, Zr and Hf exhibit the subbing effect.When only the pinned magnetic layer is targeted, the MR-improving layeras laminated above the free layer in the bottom type spin valve filmillustrated herein could be omitted. For the MR-improving layer thatacts as the underlayer for the antiferromagnetic layer herein, thepinned film constitution may have the Synthetic antiferromagneticstructure such as that mentioned above. One example of the SyAFstructure employable herein is 5 nanometer Ta/2 nm AuCu/7 nm IrMn/3 nmCoFe/0.9 nm Ru/3 nm CoFe/3 nm Cu/1 nm CoFe/5 nm NiFe/5 nanometer Ta.

[0543] In place of the Ta protective film, any of Ti, Zr, Cr, W, Hf, Nband the like is employable. Those protective films gave the same goodresults as herein.

EXAMPLE e

[0544] In this Example e, produced was a bottom type spin valve film of5 nanometer Ta/2 nm AuCu/7 nm IrMn/2 .5 nm CoFe/2.5 nm AuCu/4 nm CoFe/2m AuCu/5 nanometer Ta, in the same manner as in Example a. In this, theAuCu layer disposed between the lower CoFe layer (pinned magnetic layer)and the upper CoFe layer (free layer) is a nonmagnetic spacer layeracting also as an MR-improving layer for magnetostriction control in thefree layer.

[0545] In bottom type spin valve films, the fcc-d(111) spacing in thefree layer as formed in the nonmagnetic spacer layer of Cu or the likeis narrow and therefore the magnetostriction in the free layer isenlarged. However, in the film of this Example e in which the free layerof CoFe is laminated on the AuCu alloy layer acting as a nonmagneticspacer layer and also as an MR-improving layer, the fcc-d(111) spacingin the free layer of CoFe is controlled on a suitable level whereby themagnetostriction in the free layer could be reduced.

[0546] The spin-dependent scattering on the interface between thenonmagnetic spacer layer of AuCu and the CoFe layer is attenuated insome degree, as compared with that on the interface between AuCu and asingle-layered Cu, whereby the MR ratio in the film will decrease insome degree. This problem could be solved, for example, by using alaminate film of 0.8 nm Cu/0.8 nm AuCu/0.8 nm Cu as the nonmagneticspacer layer.

[0547] The nonmagnetic spacer layer acting also as an MR-improving layeris effective not only in the bottom type spin valve film as herein butalso in ordinary spin valve films and in dual element-type spin valvefilms. One example of dual element-type spin valve films incorporatingsuch a nonmagnetic spacer layer that acts also as an MR-improving layeris 5 nanometer Ta/2 nm AuCu/7 nm IrMn/2.5 nm CoFe as pinned magneticlayer/2.5 nm AuCu as nonmagnetic spacer layer and also as MR-improvinglayer/3 nm CoFe as free layer/2.5 nm Cu/2.5 nm CoFe as pinned magneticlayer/7 nm IrMn/5 nanometer Ta. One example of ordinary spin valve filmsincorporating such a nonmagnetic layer that acts also as an MR-improvinglayer is 5 nanometer Ta/2 nm AuCu/4 nm CoFe/0.8 nm Cu/0.8 nm AuCu/0.8 nmCu/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta.

[0548] In bottom type spin valve films and dual element-type spin valvefilms, where the fcc-d(111) spacing in the free layer of CoFe is wellcontrolled by the effect of the AuCu layer which is used as theunderlayer for the antiferromagnetic layer of IrMn or the like, anyordinary Cu layer or the like may be used as the nonmagnetic spacerlayer.

[0549] The following are other examples of bottom type spin valve filmsand dual element-type spin valve films: 5 nanometer Ta/1 nm Au/1 nm Cu/7nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nm CoFe/3 nm Cu/4 nm CoFe/5 nanometerTa, 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/3 nm Cu/4 nmCoFe/5 nanometer Ta, 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nmCoFe/0.9 nm Ru/3 nm CoFe/3 nm Cu/2 nm CoFe/2 nm NiFe/5 nanometer Ta, 5nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/3 nm Cu/2 nm CoFe/2nm NiFe/5 nanometer Ta, 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nmCoFe/3 nm Cu/3 nm CoFe/2 nm Cu/3 nm CoFe/7 nm IrMn/5 nanometer Ta, 5nanometer Ta/1 nm Au/i nm Cu/7 nm IrMn/3 nm CoFe/3 nm Cu/1 nm CoFe/2 nmNiFe/1 nm CoFe/3 nm Cu/3 nm CoFe/7 nm IrMn/5 nanometer Ta, 5 nanometerTa/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nm CoFe/3 nm Cu/3nm CoFe/3 nm CU/3 nm CoFe/0.9 nm Ru/2.5 nm CoFe/7 nm IrMn/5 nanometerTa, 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/0.9 nm Ru/3 nmCoFe/3 nm Cu/i nm CoFe/2 nm NiFe/1 nm CoFe/3 nm Cu/3 nm CoFe/0.9 rimRu/2.5 nm CoFe/7 rim IrMn/5 nanometer Ta.

[0550] In place of the underlayer of Au/Cu as in the above, othervarious laminate films and alloy layers such as those mentionedhereinabove are also employable herein.

[0551] Other examples are substrate/5 nanometer Ta/7 nm IrMn/2.5 nmCoFe/0.9 nm Ru/3 nm CoFe/3 nm Cu/2.5 nm CoFe/MR-improving layer/2.5 nmCoFe/3 rim Cu/3 nm CoFe/0.9 nm Ru/2.5 nm CoFe/7 nm IrMn/5 nanometer Ta.In this structure, the moiety of CoFe/MR-improving layer/CoFe is thefree layer, in which the constituent films are ferromagnetically coupledto each other.

[0552] In these examples, the antiferromagnetic layer is of IrMn, which,however, is not imitative. In place of IrMn, other variousantiferromagnetic materials of NiMn, PtMn, PdPtMn, RhRuMn, CrMn, NiO andthe like are also usable to produce the same good results as herein.

[0553] Spin valve films in which the pinned magnetic layer is of anantiferromagnetically coupled structure of, for example,CoFe/Ru/CoFe/IrMn (in this, two CoFe layers are as laminated via Rutherebetween are antiferromagnetically coupled to each other) alsoproduce good results of the invention. In the laminate films illustratedherein, the constituent layers each having a predetermined thickness areantiferromagnetically coupled to each other.

[0554] In the laminate films, the interlayer may be the MR-improvinglayer of the invention. For example, the laminate films are 2.5 nmCoFe/1 nm AuCu/2 nm CoFe/IrMn (in which the layers areantiferromagnetically coupled to each other), IrMn/2 nm CoFe/1 nm AuCu/2nm CoFe (in which the layers are antiferromagnetically coupled to eachother), etc. Apart from those, a laminate film of 1 nm CoFe/0.5 nmAuCu/2 nmCoFe/7 nm IrMn is also employable, in which the layers areferromagnetically coupled to each other. The AuCu layer as disposedbetween the pinned magnetic layers is to antiferromagnetically couplethe both magnetic layers to each other, while making the interfacebetween the coupled layers have mirror-reflectivity and stabilizing thelattice constitution in IrMn, whereby the thermal stability and the MRcharacteristics of the spin valve film are improved. It is desirablethat the thickness of the MR-improving layer in the spin valve film ofthat type falls between 0.5 and 2 nanometers.

EXAMPLE f

[0555] For realizing crystal structures with good thermal stability,which have few ordinary intergranular boundaries (ordinary intergranularboundaries in spin valve films worsen thermal stability of the films)but may have some small angle tilt boundaries and which are not ofcompletely single crystals, the MR-improving layer of a laminate film oran alloy layer of Au/Cu or the like is effective. One example of thestructure is thermally-oxidized silicon substrate/5 nanometer Ta/1 nmAu/1 nm Cu/3 nm CoFe/3 nm Cu/2 nm CoFe/7 nm IrMn/5 nanometer Ta. Thiswas analyzed through sectional TEM and diffractiometry. The spot size indiffractiometry was so defined that the spot diameter could cover allregion of the laminate film to be analyzed, in its thickness direction.For more detailed analysis, the spot diameter may be more reduced as inmicrodiffractiometry.

[0556] The diffractiometry of the film gave a diffraction patternindicating a single-crystal-like structure in the entire region of 1 μmor more, from which it is understood that the film seemingly has asingle-crystal-like structure. Except for Ta forming the underlayer andthe protective layer, all the layers constituting the film were infcc(111) orientation. In the diffraction pattern, another spot was seenin the site spaced from the center point by a radius, R. This indicatesthe difference in the fcc(111) spacing size between IrMn andCoFe/Cu/CoFe. In the lattice images, highly ordered fcc(111) orientationwas confirmed. Some lattice points were found discontinued in thelateral direction. In the entire region, the diffraction pattern gave asingle spot. It is believed that the lattice discontinuity will be forsub-grain boundaries such as small angle tilt boundaries.

[0557] The single-crystal-like structure confirmed herein is favorable,since the film with the structure has good thermal stability for the MRratio and the magnetic characteristics and since the structure has fewintergranular boundaries that may cause electron scattering. In thatstructure, the mean free path of electrons is long, and the peak valueof the MR ratio is increased. The technique of producing the film havingsuch a single-crystal-like structure on an amorphous substrate such asthermally-oxidized silicon or amorphous alumina is one characteristicaspect of the invention. In this Example, used was a thermally-oxidizedsilicon substrate, which, however, is not imitative. The film formationaccording to the technique of the invention may also be effected on anamorphous AlO film formed on an AlTiC substrate, or even on any otheramorphous oxide films, amorphous nitride films or diamond-like carbon.

[0558] In the film of this Example, the underlayer for Au does notalways need to be Ta. However, Au needs the subbing buffer layer of sometype. Depositing Au directly on the thermally-oxidized silicon substratedoes not give a single-crystal-like structure such as that in thisExample. As other materials except Ta usable for subbing Au, mentionedare Ti, W, Zr, Mo, Hf and alloys comprising any of them. In theunderlayer constitution of Ta/Au/Cu as herein, Ta and Au form an alloy.In this, therefore, island growth of Au is prevented, and the Au grainscould easily undergo secondary growth. In other words, the bonding forthof the grains to the substrate stronger than the aggregation forththereof has favorable influences on the film growth.

[0559] The subbing film constitution of Ta/Au/Cu is effective forpromoting single-crystal-like growth of grains. As in this case, whenthe alloying materials are formed into a laminate film, Au grains to beformed into a film do not grow as they are on Cu but form single-crystalgrains as their bonding forth to the underlayer is enlarged. Theunderlayer structure like herein could not be formed in a simple Ta/Cuunderlayer such as that in 5 nanometer Ta/2 nm Cu/4 nm CoFe/3 nm Cu/2 nmCoFe/7 nm IrMn/5 nanometer Ta.

[0560] As other examples of good layer constitution, mentioned arelaminate films or alloy films of Al—Cu, Pt—Cu, Rh—Cu, Pd—Cu, Ir—Cu,Ag—Pt, Ag—Pd, Ag—Au, Au—Pt, Au—Pd and Au—Al for Co-based magneticlayers, as in Example a. The number of layers for the laminate films isnot limited, so far as two or more layers constitute one laminate film.For Ni-based magnetic layers, mentioned are laminate films or alloyfilms of Au—Pt, Au—Pd, Au—Ag, Au—Al, Ag—Pt, Ag—Pd, Ru—Rh, Ru—Ir andRu—Pt. Like for Co-based magnetic layers, the number of layers for thelaminate films is not also limited, so far as two or more layersconstitutes one laminate film. Of the combinations of two metals, Au—Cu,Ag—Pt, Au—Pd, Au—Ag and Pt—Cu have a lot of latitude in their solidsolution. Laminate films of Ru—Cu and Ag—Cu not forming solid solutioncould also be employed herein.

[0561] Other structures of the subbing film employable herein includeTa/Cu/Au/Cu, Ta/Pt/Cu, Ta/Cu/Pt, Ta/Rh/Cu, Ta/Cu/Rh, Ta/Pd/Cu, Ta/Cu/Pd,etc. In those, the number of the layers to be on the buffer layer of Tamay be increased. In place of Ta, any of Ti, W, Zr, Mo, Hf or alloyscomprising them may also be used. It is desirable that the fcc metallayer moiety in the subbing film is not so thick if no element capableincreasing resistance is added to the film. This is for the purpose ofpreventing the MR reduction to be caused by the increase in the shuntcurrent in the spin valve films comprising it. However, if too thin, theeffect of the subbing film as a seed layer will be attenuated.Therefore, it is also desirable that the fcc metal layer moiety is nottoo thin. Concretely, it is desirable that the subbing seed layerexclusive of the subbing buffer layer of Ta or the like has a thicknessof from 2 to 5 nanometers or so. However, when an additive elementcapable of increasing resistance is added to the subbing seed layer toreduce the shunt current, the thickness of the subbing seed layer may belarger than 5 nanometers.

[0562] In place of the fcc metal laminate films capable of formingalloys such as those mentioned above, further employable herein arealloys of the fcc-forming combinations additionally containing anyadditive elements. Still other examples also employable herein are fccalloys containing Ni but not Cu, such as PtNi alloys (of which the Ptcontent is preferably larger than 26 at. % for Pt-rich alloys), RhNialloys, PdNi alloys (as being magnetic in almost all compositions,adding a third element to these is preferred), IrNi alloys (of which theIr content is preferably larger than 12 at. % for Ir-rich alloys), etc.Also for those alloys, the buffer metal may be any of Ti, W, Zr, Mo, Hfor alloys comprising them, in place of Ta. Like the laminate filmsmentioned above, it is also desirable that those fcc alloy films have athickness of from 2 to 5 nanometers. If their resistance is increased bysome additive elements added thereto, their thickness may be larger than5 nanometers.

[0563] Specific examples of the constitution discussed herein are;

[0564] 5 nanometer Ta/1 nm Pt/1 nm Cu/2 to 8 nm CoFe/3 nm Cu/2.5 nmCoFe/7 nm IrMn/5 nanometer Ta,

[0565] 5 nanometer Ta/2 nm PtCu/2 to 8 nm CoFe/3 nm Cu/2.5 nm CoFe/7 nmIrMn/5 nanometer Ta,

[0566] 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3 nmCoFe/3 nm Cu/1 nm CoFe/5 nm NiFe/5 nanometer Ta,

[0567] 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/2.5 nm CoFe/3 nm Cu/1 nmCoFe/5 nm NiFe/5 nanometer Ta,

[0568] 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3CoFe/3 nm Cu/4 nm CoFe/5 nanometer Ta,

[0569] 5 nanometer Ta/1 nm Au/1 nm Cu/7 nm IrMn/3 nm CoFe/1 nm Ru/3 nmCoFe/3 nm Cu/4 nm CoFe/3 nm Cu/3 nm CoFe/1 nm Ru/3 m CoFe/7 nm IrMn/5nanometer Ta,

[0570] 5 nanometer Ta/2 nm Cu/ 7 nm IrMn/3 nm CoFe/1 nm Ru/3 nm CoFe/3nm Cu/4 nm CoFe/3 nm Cu/3 nm CoFe/1 nm Ru/3 nm CoFe/7 nm IrMn/5nanometer Ta, etc.

EXAMPLE g

[0571] The MR-improving layer mentioned hereinabove is applicable evento artificial lattice sensors such as that in FIG. 49. In theillustrated case, the number of the magnetic layers 71 of, for example,Co-containing films or Ni-containing films as combined with thenonmagnetic layers 72 is larger than the number of the layersconstituting the spin valve film. In the case, the MR-improving layers73 are disposed each adjacent to any of the uppermost magnetic layer andthe lowermost magnetic layer. For the materials constituting the layers,the same as in Example a shall apply to this case.

[0572] The first to seventh embodiments of the invention are describedin detail hereinabove with reference to the Examples, which, however,are not intended to restrict the scope of the invention.

[0573] For example, FIG. 50 to FIG. 52 are conceptual views showingstill other modifications of the invention.

[0574] Specifically, FIG. 50 shows the cross section of a spin valvedevice part as seen from its ABS (air baring surface) FIG. 51 is aperspective view of a spin valve device with its gap film and shieldfilm being removed.

[0575] On an AlTiC substrate 10, formed are a lower shield 11 and alower gap film 12. In this, the lower shield 11 may be of NiFe, aCo-based amorphous magnetic alloy, an FeAlSi alloy or the like, and itsthickness may fall between 0.5 and 3 μm. For NiFe and FeAlSi alloys, itis desirable that the surface of the lower shield 11 is polished so thatits roughness height could be smaller than the thickness of theantiferromagnetically coupling interlayer of the Synthetic pinnedmagnetic layer. The lower gap film 12 maybe of alumina, aluminiumnitride or the like. On the film 12, formed is a spin valve device 13.The spin valve device 13 comprises a spin valve film 14, a pair oflongitudinal bias films 15 and a pair of electrodes 16. The spin valvefilm 14 may be a bottom-type SV such as that in Example 4. Briefly, itcomprises a nonmagnetic underlayer 141 of Ta, Nb, Zr, Hf or the like(thickness; 1 to 10 nanometers), an optional second underlayer 142 ofRu, NiFeCr or the like (thickness: 0.5 to 5 nanometers), anantiferromagnetic layer 143, a Synthetic pinned layer 144 offerromagnetic layer/antiferromagnetically coupling layer/ferromagneticlayer, a nonmagnetic spacer 145, a free layer 146, a high-conductivitylayer 147, and an optional protective film 148 (thickness: 0.5 to 10nanometers). On the spin valve film 14, formed are an upper gap layer 17(of alumina, aluminium nitride or the like), an upper shield layer 18(of NiFe, a Co-based amorphous magnetic alloy, and an FeAlSi alloy orthe like, having a thickness of from 0.5 to 3 μm). Though not shown, arecording part is formed thereover. The spin valve device 13 is of aso-called abutted junction type structure device, which is produced byremoving the track edges of the spin valve film 14 followed by formingthe longitudinal bias films in the removed sites. The longitudinal biaslayers 15 may be of hard magnetic films (comprising CoPt, CoPtCr or thelike as formed on a underlayer of Cr, FeCo or the like), or of laminatesof a ferromagnetic layer 151 and an antiferromagnetic layer 152 aslaminated in that order, for which the ferromagnetic layer is hardened.For the laminates, the antiferromagnetic layer 152 may be formed first,and thereafter the ferromagnetic layer 151 is formed thereon. Forproducing steep reproduction sensitivity profiles at the track edges forthe coming narrow-track devices, it is desirable that the magneticthickness ratio of the longitudinal bias ferromagnetic layer (hardmagnetic layer, or a combination of ferromagnetic layers as magneticallycoupled to each other via an antiferromagnetic layer) to the free layer,Ms×t (longitudinal bias)/Ms×t (free) is defined to be at most 7, morepreferably at most 5. If the free layer is so thinned that its thicknessis not larger than 4.5 nanometers (therefore having a magnetic thicknessof at most 5 nanometer Tesla), the longitudinal bias ferromagnetic layershall be also thinned (to have a magnetic thickness of at most 25nanometer Tesla) so as to satisfy the condition of Ms×t (longitudinalbias)/Ms×t (free)≦5.

[0576] In general, thin hard magnetic layers could hardly have highcoercive force. On the other hand, longitudinal bias layers of the typeof ferromagnetic film/antiferromagnetic film could be more firmlycoupled when the ferromagnetic layer 151 is thinner, since the magneticcoupling bias field is enlarged. Therefore, longitudinal bias layers ofthe type of ferromagnetic film 151/antiferromagnetic layer 152 arepreferred. More preferably, in the longitudinal bias layers of the typeof ferromagnetic layer 151/antiferromagnetic layer 152, the saturationmagnetization of the ferromagnetic layer 151 is nearly comparable to orhigher than that of the free layer for the purpose of realizing completeBHN (Barkhausen noise) removal in a smallest possible longitudinal biasmagnetic field. For this, NiFe alloys may be used, but more preferredare CoFe, Co and the like having larger saturation magnetization. If theferromagnetic film 151 used has small saturation magnetization and ifthe stray magnetic field is enlarged by increasing the thickness of thefilm 151 for realizing BHN removal, such will cause reproduction outputreduction especially in narrow tracks.

[0577] In the case of FIG. 50, the spin valve film 14 is not completelyetched but the antiferromagnetic layer 143 is left as it is to form thelongitudinal bias layers. Apart from this case, even the underlayer 141may be etched away. Forming the longitudinal layers 15 on the remainingantiferromagnetic layer 143 is advantageous in that the electricalcontact between the longitudinal bias layers and the spin valve film isgood. In an ordinary abutted junction structure where the length of theelectrode 16 is nearly the same as that of the longitudinal bias layer15, the electrode could not keep direct face contact with the spin valvefilm. In that case, therefore, the merit of the remainingantiferromagnetic film 143 is great. On the other hand, it is desirablethat the pinned magnetic layer 144 above the antiferromagnetic film iscompletely removed and the longitudinal bias layers are formed directlyon the antiferromagnetic film. The reason is because, as will bementioned hereunder, the magnetization direction of the pinned magneticlayer 144 must be perpendicular to that of the longitudinal bias layers15. If so, the magnetization of the longitudinal bias layers 15 will beunstable owing to the magnetic interaction between the pinned magneticlayer 144 and the overlying longitudinal bias layers 15. Alternatively,the etching removal may reach the high-conductivity layer 147 but notthe free layer, and the longitudinal bias layers may be formed on theremaining free layer.

[0578] For improving the crystallinity of the layers, or for attenuatingthe magnetic coupling force between the antiferromagnetic layer 143 andthe longitudinal bias layers 15, an extremely thin underlayer 153 (thismay be the same as the underlayer 142) may be disposed below theferromagnetic layer 151. Even though thin, a nonmagnetic layer existingbetween ferromagnetic layers will readily make the ferromagnetic layerscoupled magnetically to each other. As opposed to this, in thecombination of an antiferromagnetic layer and a ferromagnetic layer, anonmagnetic layer existing therebetween, even though thin, cancels themagnetic coupling of the antiferromagnetic layer and the ferromagneticlayer. In order to effectively apply the bias magnetic field from thelongitudinal bias layers to the free layer, the thickness of theunderlayer 153 is preferably at most 10 nanometers. For the hardmagnetic film, it is also desirable that the saturation magnetization ofthe hard magnetic film is comparable to that of the free layer. However,in general, it is difficult to prepare hard magnetic films with highsaturation magnetization of which the saturation magnetization iscomparable to that of free layers of CoFe or the like with highsaturation magnetization.

[0579] Therefore, it is desirable that a underlayer of FeCo or the likewith high saturation magnetization, of which the saturationmagnetization is comparable to that of CoFe, is formed below the hardmagnetic film to thereby keep good balance of saturation magnetizationbetween the hard magnetic film and the free layer, for the purpose ofremoving BHN in a weak longitudinal bias magnetic field. Theantiferromagnetic materials for the antiferromagnetic film 152 may bethe same as those for the spin valve film.

[0580] However, the magnetic coupling bias direction of theantiferromagnetic layer of the spin valve film must be perpendicular tothat of the antiferromagnetic film 152 of the longitudinal bias layer.(The magnetic coupling bias direction of the antiferromagnetic layer ofthe spin valve film is in the device width (height) direction, whilethat of the antiferromagnetic film 152 of the longitudinal bias layer isin the track width direction.)

[0581] For example, the two antiferromagnetic films are made to havedifferent blocking temperatures Tb. First, the magnetic coupling biasdirection of one antiferromagnetic film having a higher Tb is pinnedthrough thermal treatment, and thereafter Tb of the otherantiferromagnetic film is defined to be around a temperature at whichthe magnetization direction of the ferromagnetic film (this is pinned bythe magnetic coupling bias of the antiferromagnetic film whose Tb hasbeen previously defined) is stable and which is lower than thetemperature for the previous thermal treatment, whereby the magneticcoupling bias directions of the two antiferromagnetic films could beperpendicular to each other. For the magnetic coupling bias applicationto the antiferromagnetic layer 152, preferably used is a film-formingmethod in a magnetic field (in which is used IrMn, RhMn or the like), ora resist-curing thermal treatment method at 200 to 250° C. such as thatfor forming a recording region (in which is used PtMn, PdPtMn, IrMn orthe like). For the antiferromagnetic layer of the spin valve film, anantiferromagnetic film having a higher Tb (e.g., IrMn, PtMn, PdPtMn,etc.) may be used. In that case, the magnetic coupling bias direction ofthe antiferromagnetic film 152 could be pinned in the track widthdirection according to the resist-curing thermal treatment method,without disturbing the magnetization direction of the pinned magneticlayer of the spin valve film.

[0582] For conventional spin valve films having a single-layered, pinnedmagnetic layer, the direction of the magnetic coupling bias field forpinning the magnetic layer is disordered if the temperature for thethermal treatment for magnetic coupling bias application to theantiferromagnetic film 152 is not lowered to a significant degree. Inthis respect, conventional spin valve films are poorly practicable.However, based on the properties of the Synthetic AF structure of whichthe thermal stability for pinning magnetization is greatly stabilized attemperatures not higher than the blocking temperature of the pinnedmagnetic layer in the structure, the magnetization direction of thelongitudinal bias layer could be readily perpendicular to that of thepinned magnetic layer even when the difference in the blockingtemperature between the two antiferromagnetic films is only tens ° C. orso. Where the antiferromagnetic layer 152 is of a orderedantiferromagnetic film of PtMn or PdPtMn, it is desirable that the filmcould be ordered at resist-curing temperatures (200 to 250° C.).

[0583] It is desirable that the spacing LD between the electrodes 16 isnarrower than the spacing HMD between the longitudinal bias layers forlowering the reproduction device resistance and for realizing headsresistant to ESD. LD generally defines the reproduction track, and itmay be on a level of submicrons of from 0.1 to 0.7 μm for high-densityrecording (at least 10 Gbpsi) to which the invention is directed. On theother hand, HMD may be larger than LD by approximately from 0.3 to 1 μmso as to realize steep sensitivity profiles in the track width directionwith few influences of the hard film magnetic field thereon even thoughthe track width is narrow, thereby enabling high-sensitivityreproduction. In the condition of HD (device width)>LD and also HMD>HD,the spin valve device resistance between the electrodes can be reducedand, in addition, since the free layer in the spin valve film could havea rectangular profile of which the side in the track width direction islonger, the Barkhausen noise control is easy. Concretely, it isdesirable that the device width HD is around 0.4 μm in view of the ESDresistance of the device. For the narrow track width for which theelectrode spacing is at most 0.4 μm, it is desirable that the hard filmspacing HMD is enlarged up to about 0.8 μm.

[0584] In the case of FIG. 50 where the distance between the center ofthe free layer in its thickness direction and the surface of the uppershield is represented by gf and the distance between that center and thesurface of the lower shield is by gp, preferred is gf<gp for attenuatingthe current magnetic field Hcu to be applied to the free layer. This isbecause, since the free layer is nearer to the lower shield than to theupper shield, it is more influenced by the magnetic field from the lowershield than from the upper shield, and, in addition, since the centerthrough which sense current passes is shifted to the side of thenonmagnetic spacer 145, the free layer receives the magnetic field fromthe lower shield (this is generated by the lower shield as magnetized bysense current) in the direction opposite to the sense current magneticfield direction (see FIG. 50). With the sense current magnetic fieldbeing attenuated, a larger sense current may be applied to the device,whereby higher reproduction output and better BP are obtained, or thatis, the asymmetry in the vertical direction of the reproduction waveform is reduced. Concretely, gp may fall between 35 and 80 nanometersand gf may fall between 25 and 50 nanometers with gf<gp. In thatcondition, the gap insulation could be kept, and the total reproductiongap length may fall between 60 ad 130 nanometers to realize an extremelynarrow gap.

[0585]FIG. 52 is a conceptual view of one embodiment of a head which issuitable to the top-type spin valve film of FIG. 1 and FIG. 5. The caseof FIG. 52 differs from that of FIG. 50 in that, in the former, thelongitudinal bias layers 15 are formed on the lower gap film 12 afterthe spin valve film has been completely etched away. In the case of FIG.52, it is desirable that the distance, gf, between the center of thefree layer in its thickness and the surface of the lower shield issmaller than the distance, gp, between that center and the surface ofthe upper shield. This is because, since the free layer is nearer to thelower shield than to the upper shield, it is more influenced by themagnetic field from the lower shield than from the upper shield, and, inaddition, since the center through which sense current passes is shiftedto the side of the nonmagnetic spacer 145, the free layer receives themagnetic field from the lower shield (this is generated by the lowershield as magnetized by sense current) in the direction opposite to thesense current magnetic field direction. With the sense current magneticfield being at tenuated, a larger sense current maybe app lie d to thedevice, whereby higher reproduction output and better BP are obtained,or that is, the asymmetry in the vertical direction of the reproductionwave form is reduced. Concretely, gp may fall between 35 and 80nanometers and gf may fall between 25 and 50 nanometers with gf<gp. Inthat condition, the gap insulation could be kept, and the totalreproduction gap length may fall between 60 ad 130 nanometers to realizean extremely narrow gap.

[0586] The film constitution of the magnetoresistance effect device ofthe invention can be identified in various analyzing methods.

[0587]FIG. 53 is a graph of the data of nano-EDX analysis of the crosssection of a magnetic head which incorporates the magnetoresistanceeffect device of the invention. For example, samples for cross sectionTEM (transmission electron microscopy) are prepared, and subjected tonano-EDX with a beam of about 1 nanometer in diameter being applied tothe cross section of each sample, whereby the materials constituting themagnetoresistance effect device and the film thicknesses can beidentified. Considering the measurement limit and the influence ofinterfacial diffusion in thermal treatment, the film constitution couldbe almost reproduced. In particular, as will be understood from FIG. 53,the interface between the free layer and the spacer Cu and the interfacebetween the free layer and the nonmagnetic high-conductivity layer of Cuare relatively sharp, and the film thicknesses are easy to identify.

[0588] Regarding the definition of the film thickness, the half-valuewidth of the peak for the material of the main element constituting thefilm of which the thickness is intended to be determined is defined asthe thickness of the film. For example, the spacer Cu and thenonmagnetic high-conductivity layer (underlayer) of Cu give a sharppeak, their thicknesses are easy to determine. Based on these,therefore, the thickness of the free layer is defined as the regionsandwiched between the upper and lower Cu layers. In the example of FIG.53, the thickness of the spacer Cu is determined to be 2.4 nanometers,and that of the nonmagnetic high-conductivity layer to be 2 nanometers.The total thickness of the free layer as sandwiched between the two Culayers could be 4.1 nanometers. The thus-calculated thickness of thefree layer is to nearly reproduce the intended free layer thickness of3.7 nanometers. Through the analyses noted above, the film constitutionof the spin valve film of the invention could be identified, and thethicknesses of the spacer layer, the nonmagnetic high-conductivity layerand the free layer (even though it is extremely thin) could be measuredrelatively accurately.

[0589] The invention can be carried out in the manner of the embodimentsmentioned hereinabove, and has the following advantages.

[0590] According to the first embodiment of the invention, provided is aspin valve film with good bias point control, high MR and high ARs,which, however, could not be realized by merely thinning the free layerin conventional spin valve films. The margin for process latitude inproducing the spin valve film of the invention is broad. Thus, the spinvalve film of the invention is favorable to the coming new-generationdevices in the art.

[0591] According to the second to sixth embodiments of the invention,provided are a magnetoresistance effect device (MR device), especially agiant magnetoresistance effect device (GMR device), in which the pinnedmagnetic layer is kept stable even at high temperatures of around 200°C., and also a magnetic head incorporating the device. With coming harddisc drives being directed higher density recording, the temperature ofthe magnetic head in operating disc drives will be often high. Themagnetic head of the invention is operable at such high temperatures. Inaddition, even when electrostatic discharge current flows into the MR orGMR device of the magnetic head, the pinned magnetization of the pinnedmagnetic layer in the device is not disturbed by it and is kept stable.In addition, since the shunt of sense current is small in the device,high resistance change is kept in the device to ensure good reproductionsensitivity. Therefore, with the magnetic head of the invention, muchhigher density recording is possible, and much higher reproductionoutput can be attained.

[0592] According to the seventh embodiment of the invention, thedegradation of MR ratio in the spin valve films in thermal treatmentsuch as annealing can be prevented, and, in addition, MR ratio in thedevice can be improved through improved specular reflection in thelayers constituting the spin valve film in the device. Even when thefree layer in the spin valve film in the device is thin, the interlayerbetween the MR-improving layer and the free layer is kept stable.Therefore, after thermal treatment, the electron transmission throughthe interface is kept high, and the spin valve film can maintain high MRratio. Moreover, the magnetostriction in the free layer of, for example,a Co-based magnetic material can be reduced by the MR-improving layer,and the microcrystalline structure of the free layer can be wellcontrolled. With these advantages, the MR device of the invention ischaracterized by its high output power, few noise troubles and highthermal stability.

[0593] As has been described in detail hereinabove, the inventionrealizes high-performance and high-reliability MR devices, and itsindustrial advantages are great.

[0594] While the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

What is claimed is:
 1. A magnetoresistance effect element, comprising: anonmagnetic spacer layer, first and second ferromagnetic layersseparated by the nonmagnetic spacer layer, the first ferromagnetic layerhaving a magnetization direction at an angle relative to a magnetizationdirection of the second ferromagnetic layer at zero applied magneticfield, the second ferromagnetic layer comprising first and secondferromagnetic films antiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically so that theirmagnetizations are aligned and remain antiparallel with one another inthe presence of a magnetic field signal, the magnetization of the firstferromagnetic layer being freely rotatable in response to the magneticfield signal; and a nonmagnetic high-conductivity layer disposed incontact with the first ferromagnetic layer so that the firstferromagnetic layer is disposed between the nonmagnetic spacer layer andthe nonmagnetic high-conductivity layer.
 2. The magnetoresistance effectelement of claim 1, wherein the first ferromagnetic layer has a filmthickness between 0.5 nanometers and 4.5 nanometers.
 3. Themagnetoresistance effect element of claim 1, wherein the firstferromagnetic layer has a film thickness between a mean free path forconduction electrons having spin antiparallel to the magnetizationdirection of the first ferromagnetic layer and a mean free path forconduction electrons having spin parallel to the magnetization directionof the first ferromagnetic layer.
 4. The magnetoresistance effectelement of claim 1, wherein the nonmagnetic high-conductivity layer andthe second ferromagnetic layer have a film thickness so that waveasymmetry, (V1−V2)/(V1+V2), is in the range of negative 0.1 and positive0.1, in which V1 is the peak value of reproduction output in a positivemagnetic field signal and V2 is the peak value of reproduction output ina negative magnetic field signal.
 5. The magnetoresistance effectelement of claim 1, wherein the first ferromagnetic layer responses to amagnetic field Hin of interlayer coupling between the first and secondferromagnetic layers, a stray magnetic field Hpin of secondferromagnetic layer, and a current magnetic field Hcu of electriccurrent applied to the first ferromagnetic layer, and sum of Hpin, Hin,and Hcu is substantially zero in center of film thickness of the firstferromagnetic layer.
 6. The magnetoresistance effect element of claim 1,wherein the second ferromagnetic film is disposed adjacent to thenonmagnetic spacer layer via the first ferromagnetic film, thenonmagnetic high-conductivity layer has a film thickness t (HCL) interms of copper (Cu) layer of specific resistance 10 microohmcentimeter, the first and second ferromagnetic films have a magneticfilm thickness tm (pinl) and tm (pin2), respectively, in terms ofsaturation magnetization of 1 Tesla, and t (HCL), tm (pin1) and tm(pin2) satisfy conditions of 0.5 nanometers≦tm (pin1)−tm (pin2)+t(HCL)≦4 nanometers and t (HCL)≧0.5 nanometers.
 7. The magnetoresistanceeffect element of claim 1, wherein the nonmagnetic high-conductivitylayer is f ormed of a material having a bulk resistivity at roomtemperature not larger than 10 microohm centimeter.
 8. Themagnetoresistance effect element of claim 1, wherein the nonmagnetichigh-conductivity layer is formed of amaterial having a resistivity sothat a substantially large number of majority carriers having a spinparallel to the magnetization direction of the first ferromagnetic layerexist in the nonmagnetic high-conductivity layer.
 9. Themagnetoresistance effect element of claim 1, wherein the nonmagnetichigh-conductivity layer contains a metal element selected from the groupconsisting of copper (Cu), gold (Au), silver (Ag), ruthenium (Ru),iridium (Ir), rhenium (Re), rhodium(Rh), platinum (Pt), palladium (Pd),aluminium (Al), osmium (Os), and nickel (Ni).
 10. The magnetoresistanceeffect element of claim 1, wherein the nonmagnetic high-conductivitylayer comprises a first nonmagnetic high-conductivity film disposed incontact with the first ferromagnetic layer and a second nonmagnetichigh-conductivity film disposed in contact with the first nonmagnetichigh-conductivity film so that the first nonmagnetic high-conductivityfilm is disposed between the first ferromagnetic layer and the secondnonmagnetic high-conductivity film.
 11. The magnetoresistance effectelement of claim 10, wherein the first nonmagnetic high-conductivityfilm contains copper (Cu).
 12. The magnetoresistance effect element ofclaim 10, wherein the second nonmagnetic high-conductivity layercontains an element selected from the group consisting of ruthenium(Ru), rhenium (Re), rhodium (Rh), palladium (Pd), platinum (Pt), iridium(Ir), and osmium (Os).
 13. The magnetoresistance effect element of claim10, further comprising a layer disposed in contact with the secondnonmagnetic high-conductivity film so as to sandwich the secondnonmagnetic high-conductivity film with the first nonmagnetichigh-conductivity film and containing an element selected from the groupconsisting of chromium (Cr), tantalum (Ta), titanium (Ti), zirconium(Zr), tungsten (W), hafnium (Hf), and molybdenum (Mo).
 14. Themagnetoresistance effect element of claim 1, further comprising a layerdisposed in contact with the nonmagnetic high-conductivity film so as tosandwich the nonmagnetic high-conductivity film with the firstferromagnetic and containing an element selected from the groupconsisting of chromium (Cr), tantalum (Ta), titanium (Ti), zirconium(Zr), tungsten (W), hafnium (Hf), and molybdenum (Mo).
 15. Themagnetoresistance effect element of claim 1, wherein the firstferromagnetic layer includes a laminate film, and the laminate filmcomprises a layer containing nickel iron (NiFe) alloy and a layercontaining cobalt (Co).
 16. The magnetoresistance ef fect element ofclaim 1, wherein the first ferromagnetic layer contains cobalt iron(CoFe) alloy.
 17. The magnetoresistance effect element of claim 1,wherein the n onmagnetic spacer layer contains copper (Cu) and thenonmagnetic spacer layer has a film thickness between 1.5 nanometers and2.5 nanometers.
 18. The magnetoresistance effect element of claim 1,wherein one of the first and second ferromagnetic films disposedadjacent to the nonmagnetic spacer layer has a film thickness equal toor thicker than another one of the first and second ferromagnetic films,and a difference in magnetic thickness between the first and secondferromagnetic films falls between 0 nanometers Tesla and 3 nanometersTesla.
 19. The magnetoresistance effect element of claim 1, wherein theantiferromagnetically coupling film contains ruthenium (Ru) and thecoupling film has a film thickness between 0.8 nanometers and 1.2nanometers.
 20. The magnetoresistance effect element of claim 1, furthercomprising an antiferromagnetic layer disposed in contact with andmagnetically exchange coupled with one of the first and the secondferromagnetic films for fixing the magnetization of said one of thefirst and the second ferromagnetic films, the antiferromagnetic layercontaining XzMnl-z in which X is an element selected from the groupconsisting of iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt),palladium (Pd) and rhenium (Re) and the compositional factor z fallsbetween 5 atomic % and 40 atomic %.
 21. The magnetoresistance effectelement of claim 1, further comprising an antiferromagnetic layerdisposed in contact with and magnetically exchange coupled with one ofthe first and the second ferromagnetic films for fixing themagnetization of the one of the first and the second ferromagneticfilms, the antiferromagnetic layer containing XzMnl-z in which X is anelement selected from the group consisting of platinum (Pt) andpalladium (Pd) and compositional factor z falls between 40 atomic % and65 atomic %.
 22. A magnetoresistance effect element, comprising: anonmagnetic spacer layer, first and second ferromagnetic layersseparated by the nonmagnetic spacer layer, the first ferromagnetic layerhaving a magnetization direction at an angle relative to a magnetizationdirection of the second ferromagnetic layer at zero applied magneticfield, the magnetization of the first ferromagnetic layer freelyrotating in response to a magnetic field signal; and a nonmagnetichigh-conductivity layer disposed in contact with the first ferromagneticlayer so that the first ferromagnetic layer is disposed between thenonmagnetic spacer layer and the nonmagnetic high-conductivity layer,wherein the nonmagnetic high-conductivity layer and the secondferromagnetic layer have a respective film thickness so that waveasymmetry, (V1−V2)/(V1+V2), is in the range of negative 0.1 and positive0.1, in which V1 is the peak value of reproduction output in a positivemagnetic field signal and V2 is the peak value of reproduction output ina negative magnetic field signal.
 23. The magnetoresistance effectelement of claim 22, wherein the first ferromagnetic layer has a filmthickness between 0.5 nanometers and 4.5 nanometers.
 24. Themagnetoresistance effect element of claim 22, wherein the nonmagnetichigh-conductivity layer has a film thickness t (HCL) in terms of copper(Cu) layer of specific resistance 10 microohm centimeter, the secondferromagnetic layer has a magnetic film thickness tm (pin1) in terms ofsaturation magnetization of 1 T and the t (HCL) and tm (pin1) satisfyconditions of 0.5 nanometers≦tm (pinl)+t (HCL)≦4 nanometers and t(HCL)≧0.5 nanometers.
 25. The magnetoresistance effect element of claim22, wherein the second ferromagnetic film is disposed adjacent to thenonmagnetic spacer layer via the first ferromagnetic film, the secondferromagnetic layer comprises first and second ferromagnetic filmsantiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically, thenonmagnetic high-conductivity layer has a film thickness t (HCL) interms of copper (Cu) layer of specific resistance 10 microohmcentimeter, the first and the second ferromagnetic films have a magneticfilm thickness tm(pin1) and tm(pin2), respectively, in terms ofsaturation magnetization of 1 Tesla and, t (HCL), tm (pin1), and tm(pin2) satisfy conditions of 0.5 nanometers <tm (pin1)−tm (pin2)+t(HCL)≦4 nanometers and t (HCL)≧0.5 nanometers.
 26. A magnetoresistanceeffect element, comprising: a nonmagnetic spacer layer, first and secondferromagnetic layers separated by the nonmagnetic spacer layer, thefirst ferromagnetic layer has a magnetization direction of the firstferromagnetic layer at an angle relative to a magnetization direction ofthe second ferromagnetic layer at zero applied magnetic field, themagnetization of the first ferromagnetic layer freely rotating in amagnetic field signal; and a nonmagnetic high-conductivity layerdisposed in contact with the first ferromagnetic layer so that the firstferromagnetic layer is disposed between the nonmagnetic spacer layer andthe nonmagnetic high-conductivity layer, wherein the nonmagnetichigh-conductivity layer has a film thickness t (HCL) in terms of Culayer of specific resistance 10 microohm centimeter, the pair offerromagnetic films have a magnetic film thickness tm (pin1) in terms ofsaturation magnetization of 1 Tesla and t (HCL) and tm (pin1) satisfyconditions of 0.5 nanometers≦tm (pin1)+t (HCL)≦4 nanometers andt(HCL)≧0.5 nanometers.
 27. The magnetoresistance effect element of claim26, wherein the nonmagnetic high-conductivity layer contains a metalelement selected from the group consisting of copper (Cu), gold (Au),silver (Ag), ruthenium (Ru), iridium (Ir), rhenium (Re), rhodium (Rh),platinum (Pt), palladium (Pd), aluminium (Al), osmium (Os), and nickel(Ni).
 28. A magnetoresistance effect element, comprising: a nonmagneticspacer layer, first and second ferromagnetic layers separated by thenonmagnetic spacer layer, the first ferromagnetic layer has amagnetization direction at an angle relative to a magnetizationdirection of the second ferromagnetic layer at zero applied magneticfield, the second ferromagnetic layer comprising first and secondferromagnetic films antiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically so that theirmagnetizations are aligned antiparallel with one another and remainantiparallel in the presence of an applied magnetic field, themagnetization of the first ferromagnetic layer freely rotating in signalmagnetic field; and an antiferromagnetic layer disposed in contact andexchange coupled with one of the ferromagnetic films, a closed packedplane of the antiferromagnetic layer being oriented so that a half-valuewidth of the diffraction peak from the close-packed plane of theantiferromagnetic layer in its rocking curve is 8 or less.
 29. Amagnetoresistance effect element, comprising: a magnetoresistance effectfilm, having a nonmagnetic spacer layer, and first and secondferromagnetic layer separated by the nonmagnetic spacer layer, amagnetization direction of the first ferromagnetic layer being at anangle relative to a magnetization direction of the second ferromagneticlayer at zero applied magnetic field, the second ferromagnetic layercomprising first and second ferromagnetic films antiferromagneticallycoupled to one another and an antiferromagnetically coupling filmlocated between and in contact with the first and second ferromagneticfilms for coupling the first and second ferromagnetic films togetherantiferromagnetically so that their magnetizations are alignedantiparallel with one another and remain antiparallel in the presence ofan applied magnetic field, the magnetization of the first ferromagneticlayer freely rotating in signal magnetic field; a pair of electrodescoupled to the magnetoresistance effect film and having respective inneredges; and a pair of longitudinal biasing layers for providing biasmagnetic fields to the first ferromagnetic layer in parallel with alongitudinal direction of the first ferromagnetic layer and havingrespective inner edges, wherein the inner edges of the pair ofelectrodes are disposed between the inner edges of the pair oflongitudinal biasing layers.
 30. A magnetoresistance effect element,comprising: a nonmagnetic spacer layer; first and second ferromagneticlayers separated by the nonmagnetic spacer layer, the firstferromagnetic layer having a magnetization direction at an anglerelative to a magnetization direction of the second ferromagnetic layerat zero applied magnetic field, the magnetization of the firstferromagnetic layer freely rotating in a magnetic field signal, amagnetoresistance effect-improving layer comprising a plurality of metalfilms and disposed in contact with the first ferromagnetic layer so thatthe first ferromagnetic layer is disposed between the nonmagnetic spacerlayer and the magnetoresistance effect -improving layer, one of theplurality of metal films disposed in contact with the firstferromagnetic layer contains metal element of not solid solution withmetal element of the first ferromagnetic layer; and a nonmagneticunderlayer or a nonmagnetic protecting layer disposed in contact withthe magnetoresistance effect-improving layer so that themagnetoresistance effect-improving layer is disposed between the firstferromagnetic layer and the nonmagnetic underlayer or the nonmagneticprotecting layer.
 31. A magnetoresistance effect head, comprising amagnetoresistance effect element having a nonmagnetic spacer layer,first and second ferromagnetic layer separated by the nonmagnetic spacerlayer, the first ferromagnetic layer having a magnetization direction atan angle relative to a magnetization direction of the secondferromagnetic layer at zero applied magnetic field, the secondferromagnetic layer comprising first and second ferromagnetic filmsantiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically so that theirmagnetizations are aligned antiparallel with one another and remainantiparallel in the presence of an applied magnetic field, themagnetization of the first ferromagnetic layer freely rotating in amagnetic field signal; and a nonmagnetic high-conductivity layerdisposed in contact with the first ferromagnetic layer so that the firstferromagnetic layer is disposed between the nonmagnetichigh-conductivity layer and the nonmagnetic spacer layer
 32. Themagnetoresistance effect head of claim 31, further comprising upper andlower magnetic shields sandwiching the magnetoresistance effect elementthrough respective one of upper and lower magnetic gaps, wherein anaverage surface roughness of an upper surface of the lower magnetic gapis smaller than thickness of the antiferromagnetically coupling film.33. The magnetoresistance effect head of claim 31, wherein the distancebetween a center of film thickness of the first ferromagnetic film andone of the pair of magnetic shields through the nonmagnetichigh-conductivity layer is equal or smaller than a distance between thecenter of film thickness and another one of the pair of magnetic shieldsthrough the second ferromagnetic film.
 34. A magnetic recording andreproducing head, comprising a magnetoresistance effect element having anonmagnetic spacer layer, first and second ferromagnetic layersseparated by the nonmagnetic spacer layer, the first ferromagnetic layerhas a magnetization direction at an angle relative to a magnetizationdirection of the second ferromagnetic layer at zero applied magneticfield, the second ferromagnetic layer comprising first and secondferromagnetic films antiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically so that theirmagnetizations are aligned antiparallel with one another and remainantiparallel in the presence of an applied magnetic field, themagnetization of the first ferromagnetic layer freely rotating in amagnetic field signal; and a nonmagnetic high-conductivity layerdisposed in contact with the first ferromagnetic layer so that the firstferromagnetic layer is disposed between the nonmagnetic spacer layer andthe nonmagnetic high-conductivity layer; and a magnetic recording headcomprising a magnetic pole and a coil for providing said magnetic fieldsignal to the magnetic pole.
 35. A magnetic head assembly, comprising amagnetoresistance effect head including a nonmagnetic spacer layer, andfirst and second ferromagnetic layers separated by the nonmagneticspacer layer, the first ferromagnetic layer having a magnetizationdirection at an angle relative to a magnetization direction of thesecond ferromagnetic layer at zero applied magnetic field, the secondferromagnetic layer comprising first and second ferromagnetic filmsantiferromagnetically coupled to one another and anantiferromagnetically coupling film located between and in contact withthe first and second ferromagnetic films for coupling the first andsecond ferromagnetic films together antiferromagnetically so that theirmagnetizations are aligned antiparallel with one another and remainantiparallel in the presence of an applied magnetic field, themagnetization of the first ferromagnetic layer freely rotating in amagnetic field signal, and the magnetoresistance effect head alsoincluding a nonmagnetic high-conductivity layer disposed in contact withthe first ferromagnetic layer so that the first ferromagnetic layer isdisposed between the first ferromagnetic layer and the nonmagnetichigh-conductivity layer; and an suspension arm holding themagnetoresistance effect head.
 36. A hard disk drive system, comprisinga magnetic medium, and a magnetic head assembly, comprising amagnetoresistance effect head for reproducing magnetic signal field fromthe magnetic medium, having a nonmagnetic spacer layer, first and secondferromagnetic layers separated by the nonmagnetic spacer layer, thefirst ferromagnetic layer having a magnetization direction at an anglerelative to a magnetization direction of the second ferromagnetic layerat zero applied magnetic field, the second ferromagnetic layercomprising first and second ferromagnetic films antiferromagneticallycoupled to one another and an antiferromagnetically coupling filmlocated between and in contact with the first and second ferromagneticfilms for coupling the first and second ferromagnetic films togetherantiferromagnetically so that their magnetizations are alignedantiparallel with one another and remain antiparallel in the presence ofan applied magnetic field, the magnetization of the first ferromagneticlayer freely rotate in a magnetic field signal, and themagnetoresistance effect head also including a nonmagnetichigh-conductivity layer disposed in contact with the first ferromagneticlayer so that the first ferromagnetic layer is disposed between thenonmagnetic spacer layer and the nonmagnetic high-conductivity layer;and a suspension arm holding the magnetoresistance effect head so thatthe magnetoresistance effect head is disposed on or above the magneticmedium.